I just read in the V21.1 balance patch thread that the game is set to be around 6 months game time in length, since we start in September I guess that means we can end it roughly in march, and I'm sure like the original we won't have to end it, we can just keep on fighting aliens.
For me personally that's too quick. So I'd like to suggest something from the new "X-Com" (I use that term loosely), and that is Marathon mode. I never used it and to my understanding it's a bugged feature but it supposedly extends the game length by three times. Now that's way too long and making research take three times longer just doesn't sound like fun. However there could be a few balances in place: the invasion now takes a year, research time is the same but more advanced ships with more advanced researchables don't come until later (corvettes appearing in January instead of November/December). I'm fine with the game setting as it is and I'm sure I could probably mod the change I want (probably) but 6 months seems way too quick for me!