One important thing wasn't really discussed here: Playercount (and Map size)
From what we have seen there are small maps (strike zone), large maps (whiteout) and medium ones (chasm, and that desert one) - overall I would say maps have similar sizes than in MW2/MW3, slightly larger (or at least less clustered) than BO2. So how many players per server would be good? What number of players works best for this game?
Public play in previous games has always been 6 vs. 6 and 9 vs. 9 in ground war. Personally I think 6 vs. 6 or maybe even 4 vs 4 (like in BO2 League) was a good number for most maps. Too low for the largest maps and too high for the very small maps though. It also depends on the gamemode of course.
What does this have to do with servers? Well since matchmaking allowed voting for maps, there was ALWAYS the smaller map that was voted. And if you look at server browsers (BO1, 4D1) there are lots of games on either small maps or with extremely high playercount (32+).
What would be the best number of players for OPs server setup?
In the past (most) maps were optimized for 12 players (and still will be on consoles) so how would that work on PC if you have 24-32 (64 is impossible imho) players on a custom dedi? Also if Vanilla servers are locked to 12-18 players, it would be a big difference to the custom servers which would most likely run with higher numbers. I'm not sure if the maps are large enough for custom dedis.
I'd really like to see scalable maps in the future with 3-4 different sizes available. So basically depending on playercount/gamemode, more ore less parts of the map are available, similar to how it worked in Battlefield, but on a much smaller scale. This could solve the "no one votes for large maps" problem because all maps can be the same size.