I think I'll have a go at this then =D, going up to 2015:
End of 2011:
Some of WoW's subs have dropped to play some of the newer MMOs - 9.5million subs
With the release of GW2, SWTOR and Tera, Rift is no longer the only alternative to WoW, subs drop to under 1million
SWTOR had a strong launch with around 4 million people trying it out, but after a month or two 1.5 million subs stayed.
GW2 starts with one million subs and hits the 1.5million mark, bringing it level with SWTOR
Tera starts off small with only around half a million subscribers, but the subs gradually grow
2012:
The novelty of some of the new MMOs wear off, WoW at 11 million subs.
Rift is now at half a million subs, and those numbers remain persistent throughout the year.
SWTOR is down to 1 million subs as people return to WoW or decide to see some of the other newer MMOs
GW2 starts getting more popular and hits 2 million subscribers
Tera is now level with GW2 at 2 million subscribers
2013:
An expansion was released in december 2012, it involves going to Argus and defeating the legion. Most of WoW's subscribers stay knowing they might as well make the most of what they predict to be the last expansion, but not much new people join as there's plenty more MMOs out there by now. 11million subs.
Rift's first expansion has been released. Players return, and more players are attracted to the game, and not before long Rift's at 1 million subs.
SWTOR now has under a million subs. BioWare decides a whole new game is needed as SWTOR was originally too similar to WoW. This isn't a Mass Effect or Dragon Age MMO, it's a completely new franchise.
GW2 and Tera are both at around 3.5 million, both taking subs from SWTOR players who've left the game.
2014:
WoW nears it's final content patch, but a lot of players aren't sticking to their plans of just staying to the final expansion as the game is extremely outdated. Subs drop back down to 9 million.
Rift first expansion was a success for the the first half of the year, getting the game up to 2 million subs. But in the second half of the year, it's too much of the same and subs drop back down to 1 million.
Titan is now out, and it's off to a strong start with 5million subs!
SWTOR has some pretty pathetic content patches to keep the player base going until the new MMO. But it seems BioWare won't have an MMO until their new one is released, as SWTOR is becoming unpopular, and soon has little subs. Bioware make it f2p and don't touch the game. Now that all the SWTOR devs transfer to the new MMO, things will happen a lot quicker.
GW2 goes down to 3 million subs and stays that way all year
Tera is down to 2 million subs. It almost has no Korean players, so the devs are losing faith in the game.
2015:
After the final content patch, WoW's subs moved to Titan and other MMOs. There are only about 1 million players left. The game is now f2p. By the end of the year, WoW is dead. WoW was not killed by any game in particular, it was just finished when Blizzard chose to finish it.
Rift is now back down to how it was before the first expansion. Later in the year, Trion announce they don't have the funds for a new expansion. They say they'll most likely make single player games, and when they have the money, they'll start developing a Rift 2.
Titan is growing quickly, especially now a lot of WoW's subscribers have stuck with Blizzard and went to Titan. 8.5 million subs already.
SWTOR basically dead. Bioware says their new MMO will probably be released late 2017.
GW2 is having a content filled expansion this year with the most content an MMO expansion has ever seen. People get excited for this, and the subs raise to 6 million three months into the expansion.
With no Korean subs, Tera is abandoned by the devs. The 2 million remaining subs are enjoying f2p content, but after a few months they get bored of the game without patches or updates and they leave