Quick meta-input:
It's largely true that we haven't changed gameplay significantly since forever. The main cause of this is that not a great deal of people on the team actually play the game, and the few that do seem largely content with the breakneck speed and the current mechanics. There is a metagame, and it's a relatively simple one since it's rather poorly balanced on the whole.
Furthermore, many devs feel that changing something now is useless since we're still in Alpha. Now this is something on which I could complain at length, but it's there.
Personally, I believe we're a little too hung up on Age of Empires - and my personal preference would be for a complete switch to a production/consumption system over the "one shot" AoE like system of gathering resources. Each unit would consume some resources, each unit would produce some, and houses would give you manpower instead of raising the pop cap (which would then be soft-capped). On the whole it'd make eco more interesting.
I also generally agree that the game goes way too fast in the early stages and that units are inherently too cheap, but that is definitely a matter of personal preference - and many would argue that AoE 2 goes way too slow. We've also had weird effects at play, such as the big unit speed and very large vision ranges, making our maps feel extremely small.
Relatedly, our counters are crap - that's because we have far too few units per civilisations, and made some braindead decisions such as the pierce/hack attack we chose.
But to go back to my first point: even perfect mods won't be played much, since the team doesn't play much, and that means that imperfect mods (such as my trade changes) have basically 0 chance of convincing anybody.