Do people actually play 4x games with strangers? Those games last so long I figured you'd only play with people you actually knew, otherwise idiots could just come and go all the time defeating the purpose.
Diplomacy with people you know has a huge drawback:
Grudges are carried from one game to another, which kind of defeats the purpose of diplomacy.
I would rather only play team games with people I know to avoid the metagame issue.
Random people do drop from games, but usually when their position is hopeless anyway, so it is usually not a big issue if what is left of them is given to the AI.
One of the big issues with turn based MP 4X is that in order to work in MP, they really need to allow simultaneous turns without butchering the gameplay.
AoW, Civ and Gladius both support simultaneous turns, but in an engine in which it does not make any sense (ie, it encourages waiting the end of the turn to move twice in a row, or at the very least, makes execution speed important in a game in which it should not happen).
That is why Dominions works better than the most here. It was planned from the beginning with MP and simultaneous turns in mind.
Without that, even by email with turn due dates, it can take forever to play.
The other issue is tactical battles.
They are cool in solo, or in a 1v1 game. But as soon as you add more players, it forces people to either:
take an almost infinitie exchange of emails to get the battle done, arrange a time to play live, and/or have the other players be forced to do something else.
That is why I never could get into MOO2 in MP. Waiting for other to play their battles was not super interesting, and playing without tactical battles butchers the game.
The problem is that there are not that many games left:
Dominions,
Armada 2526 (but I doubt it has any community),
The RT 4X (Paradox, or Sins of a solar Empire and Kohan. The latter doesn't have any community at all).
Star Wars Rebellion (RT + 2 players gets rid of most of the issues, but it doesn't have any community either).
Diplomacy and other ported board games or war games (actually, most board games are meant to be finished in a single sitting, so they are usually a good fit).
Solium Infernum (but the UI and use of Adobe Director are bad).
Something that would work would be a team based 4X in which you could delegate units to your team mates in tactical battle, but I am not sure there is any.
Neptune's Pride and other Web based 4X also work. Many of the web based ones are tick based, which works with long ticks.
2 hours ticks or less should definitely be avoided, as it forces you to check things constantly, and at night.
Also, ongoing games that last for years are not super healthy, but can be cool if you are in college (I spent thousands of hours in Hyperiums, doing shifts during the night with guidmates, and ended up playing the last year because I felt I had a responsibility to stay before I stopped for good). It is basically Eve Online but at a larger scale.
Fondation: Le Jeu is also cool once you "graduate" past the early stage, and has 2 weeks campaigns combined with a meta progression, which is a good compromise. But it is only in French (I think), and suffers from the 3AM alarm syndrom.