I am not quite sure what you are talking about here? What forces a switch to Redistribution?
If you hadn't brought this to my attention I'd have never gotten the chance to reread and also wonder what Im heckin talking about too. I just now realize these confusing statements had been deprecated by novel thoughts that crystalized as I was writing but I failed the critical Proofread. Therefore disregard. Will Edit for Strikethrough. For the sake of Sheez n' Geez I was trying to outline what on reflection now reads like the DoC version of a Conspiracy Theory; that is, having run out of rational explanations for what seemed deranged to me, it was left to suspect some bugginess was afoo
The only mechanisms to forced civic switches I can think of are espionage, UN, and losing ability to run the civic (e.g. never having had the tech). Only the latter is really applicable but that should result in a switch to Reciprocity.
First note: this should be implied by above statement but Reciprocity is the civic in question (my regrets; spamming these similar multisyllabic Re- Words must have spun me around). I concur on the known causes and the following add up to sufficiently justify trying out the premise that there is an unknown cause responsible for the shift (I guess this is what "forced" w/ quotes was a placeholder for): UN is obvs ruled out (too early), reported instances of revert to Reciprocity occurred far too early in the game to take on Espionage as a candidate explanation, and after extra checks to make dang sure I didn't make another booboo and forgetting a suspected civ didn't start with Recip, we may safely proceed with holding true that these were indeed cases of an unelected (aka forced) Civic change. Further confidence was lent to the Buggery Thesis by the admittedly confused account you quoted.
I'll try again with an illustration of an observed example: running autoplay, check Info and notice HRE is on Reciprocity seemingly out of nowhere, and make the casual notice that two other civics different from spawn. CTRL+C to check log for Revolution dates and see only one, reload earlier save and rerun, this time actively monitoring for expected Civic switch. Sure enough it occurs on or close to first occurrence, *except* this go-round HRE ends up with Redistributrion, which of course is a legal choice. Parallel cases have been witnessed (illegal switch to Recip associated with legal Civic change) but I've yet to perform similar diligence, and still more is due to narrow down the Code Criminal stirring up the mischiefs.
The evaluation of trade value is not very good currently, I think it only accounts for the number of cities multiplied with a constant factor, without taking things like city trade modifiers or relationship modifiers into account.
Reading this prompted an instant Leo-DiCaprio-Pointing-At-TV: this is where I'd start any investigation and experimentation.
People have also raised the point that Merchant Trade is not very good at a time where it is the only other alternative. Moving Regulated Trade extends that window.
Hundo P concur both on judgements of MT's merits and the desired goal. Indeed it looks like the appropriate vector is to work on strengthening MT, even setting AI concerns aside for the moment.
If Merchant Trade is genuinely not attractive enough, what could be done?
This lil runt of a question has been a persistent bee in my bonnet for a I-Dont-Know-How-Long.
Reduce upkeep to None: would fit thematically, establishes a greater upkeep difference with Redistribution, easy to implement. Downsides are that it would reduce its upkeep below Free Enterprise and once again would mostly benefit large empires.
Concur.
Maybe Redistribution should go to high upkeep instead?
!!! The very same idea hit me when I finally read the Pedia entry to get a better handle on what its supposed to represent.
Allows trade routes without open borders:
OMG STOP READING MY MIND
The third one seems to be the best out of those ideas, to be honest.
As things stand, I'm with you.
For the sake of focusing my own thoughts and maybe others' I'm going to present my capitulation of what "Merchant Trade" encompasses: As opposed to the movement, exchange, dissemination, cultivation, etc. undertaken by what we may consider a State apparatus of any level of sophistication, operating in principle with a singular, focused, and organized intent, in this case these and similar outcomes devolve on the activity of effectively autonomous individuals and/or more or less informal but discrete associations thereof. Characteristic effects of such arrangements include the following. The discharge of any State or Ruling apparatus from any necessary commitment, involvement, or costs toward the listed outcomes without the total concomitant surrender of benefits that may ensue as a result. Within such a decompartmentalized and unburned system, availability of goods tends toward greater diversification and variety for those with access to its offerings so long as these are available; conversely, subordination of the availability of staple goods to disinterested forces exposes participants to the fullest extent of disasters, shortages, price swings, etc. A necessary downward movement of wealth occurs and an associated redistribution of political power can be expected to follow as outside circumstances and vicissitudes permit, though the downward limit of both can necessarily fall no further than the merchant class itself (aka Oligarchy). Competition within these locuses of power may find expression in unexpected areas such as patronage, public beneficence, and civic leadership. Being comprised mostly of independent and far-reaching agents whose endeavors are served by the pursuit of information in a Zero Sum arrangement, a consequent dissemination and evolution of knowledge and ideas ensues. (My sincerest apologies for So Much Extra but once my feet hit the ground I couldn't help sprinting off so therefore also my most genuine thanks for reading).
TLDR; Moar Stuff Reaches Moar Places, But Mo Money Maybe Mo Problems
An Espionage association (the Mercantile rumor mill; "tales from the east", as it were) hit me as a thematic fit but struggling to find notable value for its relevant timespan unless the bonuses are quite considerable; already I could foresee balance problems or AI goofery (spy spam, Slider silliness) arising that could be a challenge to reign in. Building Production Speed tends to be hard to go wrong with as an effect, shuffling associated Buildings among other Civics would be a snap and I'd propose these may warrant review in any case (e.g. Big Chads with Big Money shell out for "luxuries" like Libraries and Theatres. They're also known to Sugar Daddy for Art Geeks and Tech Nerdz) . No idea if/how something like this were implemented, but could trade routes generate Map knowledge? Or short of this they would maintain contact?
. Also remember that, even for large empires, a larger capital population is the best way to combat overextension. So even with large empires Redistribution can play an important role.
Let's begin:
per population wouldn't be a bad idea, seeing how "+50% 
to finish civilian unit production
on unimproved, camp, pasture; Excess 
per specialist
; +10% 
a bit more.
in all cities; Double Priest slots
citizen
; If pagan, can still construct pagan wonders if a religion spreads to a city
; Double Scientist slots
from corporations was very fitting.
