I think the Taj Mahal is fine as is.
I do not find it superfluous.
Maybe I'll keep it's Golden Age but give it something else in addition. I don't want it to feel weaker than the Unique Wonders, especially given its more expensive than many of them.
I would be glad if there were some thought given to ways to improve the very end of the tech tree for those of us who do not play with the space race. (I got sick of it as soon as other victory options became available in ?Civ II?) Usefully extending the tech tree to current day and 40 years beyond would take a lot of work, but I think it would be worthwhile. (I assume there are other mods that might help with this.) I hope this can get on the list of things to do eventually.
In this context, it might be easier to find a useful role for late wonders such as LHC.
I don't wish to expand the Future era into a full-fledged sci-fi era like many mods do. I do agree that there should be a few interesting 'bonus' items available there for the player that manages to reach it. Not a priority at the moment but definitely something for the todo list.
While I suspect 3 choices should be enough, 5 might be slightly better.
I assume what one could do is multiply all tech costs by factor, which would be 1 for the default setting.
The way I'd have implement this would be via new gamespeed options. So for example, there might be 'Marathon' and 'Marathon (faster research)'. There's really only space for one alternate setting either side of each main gamespeed or they start crossing over into each other which makes little sense. It might be worthwhile providing some alternate production speed options too.
The cost of doing so, of course, is an artificially depressed science rate, and techs which are inherently expensive because of the larger map and civilization size (I think; is that how they work?).
Yep, research rate scales by both gamespeed and mapsize. The AI's rate also scales by difficulty level.
One thing I think IS missing from research in History Rewritten is the monastery. In vanilla Civ IV, you get the technology to build them very early in the game, there's a strong incentive to build them for culture, for missionaries, and for science. If you're diligent about spreading religions through your empire*, that adds up to a 10% or 20% bonus to science production in most of your cities, possibly even more in the large central ones if you go out of your way to spread minority religions to them.
In History Rewritten, that bonus isn't available until some time in the Medieval period, so the only science boost you get is the one from libraries- in effect, something like 15% of the science production I usually have in the Classical and Medieval periods isn't there in HR.
Yeah, I made a deliberate decision to have religion be one of the major elements of the Medieval era. I suspect I need to make the benefits of religion, particularly the shrines a bit stronger though, because of this delay. Shifting the monastery research bonus later is a side effect of that.
I understand that you don't want civilizations spamming missionaries until a bit later in the game, but maybe we can come up with an early-game improvement that provides a limited science bonus to offset the lack of the monasteries? Perhaps something that offers a 10% or 20% increase, while removing the bonus from monasteries or decreasing it from 10% to 5%...
I'm certainly not adverse to adding more sources and modifiers for research but I think it would be best to see how the calendar changes and gamespeed tweaks feel first.