My plans for the next upgrade:
(1) Switch the starting techs of Commercial and Scientific civilizations, so that Commercial civs start with Mathematics and Scientific civs start with Writing. That really doesn't make any more inherent sense than the current arrangement, but will facilitate my next change....
(2) Set all trait-specific small wonders to require prerequisite improvements. Four of them already do require buildings available with starting techs; those four will now require that you have at least two cities. The other four small wonders will require prerequisite improvements in only a single city, but which you'll only be able to build once you progress a bit in the tech tree. The commercial small wonder will require that you have a marketplace, and the scientific small wonder will require a library. (Thus the switch in starting techs noted above; it makes these requirements a bit more logical, as they'll be linked to techs that stem from the correct starting techs.) The industrial small wonder will require a smithy. I'm not entirely sure about the expansionist small wonder, since the Wheel doesn't lead to *any* tech that allows you to build an improvement, but I'm thinking that requiring worker housing makes about as much sense as anything.
(I can't link these small wonders to techs because they're already linked to techs. They're just not linked to techs that appear in the tech tree.

And I don't want them linked to resources, as they're supposed to be available based solely on civ traits. But linking them to prerequisite buildings as described above should take care of the problem -- and I agree it *is* a problem -- of being able to build some of them on Turn One.)
(3) Set all trait-specific small wonders that don't already do so to produce units. (Other benefits may have to be toned down a bit to retain balance.) The seafaring small wonder will produce ocean-capable vessels, with stats and speed most likely between those of a curragh and a galley. The military small wonder will -- big surprise! -- produce fighting units, most likely just warriors. (They can, of course, be upgraded just like any other warriors, so they're not useless. Just free.) I'm not sure about the scientific and commercial wonders, but if all else fails, well, workers are always handy!
(4) Set all trait-specific small wonders to expire with Medieval techs. (The seafaring wonder, for example, will expire with Astronomy, which allows deliberate creation of ocean-capable vessels.) Having them keep churning out units 'til Doomsday just seems a bit ridiculous.
(5) Rename the scientific small wonder, since calling it the "Philosopher's Forum" is a bit problematic if it's built before Philosophy is discovered.
(6) Disable the upgrade from privateers to destroyers. Privateers will now be a "dead end," and will fade from usefulness as other naval vessels upgrade into the modern era. Yes, modern piracy exists, but the more I thought about it, the more I realized that it's aimed mostly at smaller vessels, which aren't represented in the game. In the days of classic piracy, when men such as Blackbeard, Long John Silver and Captain Jack Sparrow ruled the oceans, pirate vessels could attack even naval fighting vessels with something at least vaguely resembling parity. But I doubt any modern pirates have ever seriously contemplated taking on a battleship.
(7) Add a new "primitive" tank -- most likely Ripptide's WWI "1918" tank unit -- available with Combustion, which will upgrade to the currently-available tank, and serve as a bit of a "bridge" between cavalry and tanks.
(8) Disallow settlers from goody huts.
(9) Set Machiavelli's wonder to produce assassins slightly less frequently.
(10) Adjust the expiration tech for Slave Trade. I'm not sure why I set it to expire with Medicine. I need to come up with a more logical choice.
I'm not going to mess with additional trait-linked abilities right now, as I'm undoubtedly going to be opening a huge can of worms when I do. But I'll give the idea some more thought.
I'm also not going to worry about adding a wonder linked to the Piracy tech, though I still think it could be fun.
If you've any comments on any of those plans, speak now before I actually implement them!
-- Darryl