I added one more, very logical progression for BF that'll attract thousands and thousands of more players:
Introduce a more MMO(-ish) experience.
Imagine a 50 v 50 or 64 v 64 server, or skew that number with a 32 defenders v 96 attackers server with an Operation Overlord D-Day Normandy beach invasion as its highlight. A huge player count is a massively desirable feature to the BF franchise, and it would be a huge upgrade. The mere thought of playing a huge D-Day map with a 100+ player count is something that players can immerse themselves into. We can do the same for an "Eagles Nest" game mode where a relatively few player count defends a high point against a huge horde of attackers.
We can even go bigger and have a crazy MMO "Grand Event" wherein it's a 200 v 200 (or 100 defenders v 300 attackers) server one weekend a month. This'll engage gamers even more and they'll feel the intensity of the invasion of Normandy or other operations by magnitudes more. This will attract a huge gamer crowd, new or otherwise, and keep everyone on their toes.
Competitive gaming and huge cash prizes
It's obvious to me that EA / DICE is trying to break into the e-Sports world with the BF franchise, with a hard focus on squads as teams. Cash prizes and a hugely competitive experience will draw in larger crowds. The big challenge, of course, is that the right format and execution are crucial. Will we see this with BF's version of Battle Royale? Other game modes we currently have? A brand new, unannounced mode altogether? We saw this attempt with BF1's Incursions mode, but it didn't jibe well (for me, it had a large part to do with the fixed classes and preset loadouts that didn't allow for enough customization).
