I think the qualitative revolutions made in civ6's tech trees when you unlock things like "can put units on water" or "can dig a canal" are something we need more of, especially int he realm of traders. Let this or that tech allow me to do something I simply couldn't before. I would actually prefer if you needed some kind of containerization civic before you could do hybrid land/water trade routes (water being city on coast or with harbor to another city on coast or with harbor.) Until then you can be stuck hopping up ports on the coast or plodding through a trading post network across the continent.
This is a place to go into detail just a bit on the kind of Interactive Changes I was talking about.
You could always shift cargo from sea to land transport or back again - but every time you did that, there was wastage: boxes broken in handling, cargo dropped overboard by mistake, stolen, etc. In game, that should translate as a drop in Bonus from any Trade Route for every such trans-ship point - which would not completely offset the mighty boost from having a Sea Trade Route, but diminish it.
Until the 1950s (mid-Atomic Era) when everything not bulk raw materials could be loaded into a standardized Container at the point of origin and that container sealed and unsealed at the destination, moving by way of railroad, road, sea or air as required in between. Losses in transit drop dramatically, speed of transit goes up, profits and amount of goods traded rises spectacularly using the same facilities - ports, rail yards, trucking depots - already in existence, but modified to take advantage of the new methods. Add to that computerized international communications and shipment tracking, and you also revolutionize Manufacturing: no more depots and warehouses and yards full of raw materials to feed the production lines, everything can be shipped to the producing facility as needed, with assurance that it will arrive precisely when needed. That also means the speed with which manufacturing can react to changes increases dramatically: the factory does not have to work through a backlog of parts and materials: change the machinery (which is increasingly multi-purpose and automated), start shipping new raw materials, and shift output from Televisions to smart phones, automobiles to light trucks, in weeks or months instead of months or years.
So, one Atomic Era change results in changes to Trade, Gold income from trade, Production - and also makes possible the buying and selling instantly on-line, since goods can be shipped in virtually any quantity anywhere at a moment's notice, so it also changes Amenities and adds value to existing Harbors, Commercial Hubs, Industrial Zones, Markets, Factories, etc.
And it's all missing from the game, and it's only one example of what's missing from the game.
One more quick example (sorry, but I'm On A Roll here)
In World War Two, both the German and US armies estimated that it took 8 - 13 shots from a medium tank to knock out an enemy tank, at an average range of 700 meters.
20 years later (1965 - Atomic Era) a NATO medium tank with the then-standard 105mm canon could knock out an enemy tank with at most 2 shots, and could virtually guarantee getting a hit with the second shot, at ranges up to 1500 meters. So, the lethality of the 'Modern Armor' had increased by at least 300% and the range doubled since the 'Tank'. Not counting, of course, that the average speed of the Tank was about 40 kph, of the Modern Armor 50 kph with twice the range on a tank of fuel, and 2 - 3 times thicker armor.
20 years after that (1985 - 90) the main gun was now a 120mm cannon, the armor was a complex composite of metal, ceramic, and plastic, the speed was up to 70 kph, and enemy tanks were being hit at 3000 meters, or 4 times the WWII range. Not to mention that the tanks had fire suppression systems, night vision, could fire on the move at speed and communicate with HQ through satellite links over 1000s of kilometers.
In other words, we're missing at least one more Upgrade in the middle of the Tank - Modern Armor progression, BUT adding more units that late in the game is, right now, a waste of design resources.
So, the End Game (Atomic Era plus) needs a major rethink, to even slightly-accurately model the changes that have taken place. Adding a few 'modern techs' doesn't do it: there are Massive Changes in almost every aspect of the Cultural, Trade, Amenity and Domination game that need to be addressed. Right now, the late game appears (to me, who has lived through most of the Atomic and Information Eras) Unfinished, even an afterthought to the game.
