As I see it, Modern Era gameplay has several issues we need to take care of. A Tech Tree revamp can serve as the spearhead to deal with these issues.
(1) A well-developed post-Assembly Line economy will have excessive Production. There will simply be no buildings left to build. This is the real reason why Space Victory is introduced - because if you're not building military for Conquest/Domination you have very little else to build.
This can be negated by:
(1A) Introducing new Buildings via existing or new Techs;
(1B) Introducing new Wonders/Projects;
(1C) Introducing new, more modern units via existing new Techs.
(2) A less-than-realistic Great Depression mechanics. The current Great Depression code (inherited from Rhye) only take into consideration Yields, and disregard Commerce from Specialists or Companies. This needs to be changed given the very effective Companies in DoC.
(3) A less-than-realistic Global Warming/Random Events mechanics. There are many existing mods for these. We need to borrow/absorb some of them to make the Modern Era more realistic and challenging.
(4) Post-Medicine Plague mechanics. We need something to simulated modern epidemics like SARS and Bird Flu, and its effects in disrupting international Trade.
That is all I can think of at the moment. I have always felt that the Modern Era in Civ IV, RFC, and DoC are somewhat crude and incomplete, which is why I very seldom play past 1800 except as America (which I almost never play past 1930).
However, there is much potential in a Modern Era focused RFC. All the existing mods (RFCE, SoI, Greek World, Classical World, DoC itself) are focused on eras before the Modern Era. It's precisely because the framework of Civ IV and RFC needs to be expanded to provide realistic and challenging Modern Era gameplay.
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