Actually he can. WoW has several full retail packaged expansions with another one due soon. All he has to do is price those updates at full retail and put less content in them so he can release them yearly. If you are already paying a subscription then it's highly likely you will be prepared to also buy those yearly updates. Or at least thats what I assume is bubbling in the back of his mind.

New microtransaction concept - pay per helicopter (PPH). They make the game free to play, but charge you $1 every time you see a helicopter. Sounds good at first, but by the time you're finished with the CoD4 campaign, you've ended up paying7.
It also creates a new metagame wherein you have to avert your eyes whenever you hear the sound of rotors.

This is why we need more evil in the world.dam fucking paladins ruin everything.
we need a plan to stop this.
plan a:Rush in there with a army of minions kill everyone who does not bow to are will.then kill are quest goal.
[alymay walks in to the rule]
alymay:what about a spider?
me:For the last time we are not going to use a spider.
alymay:O.o this gives me a idea for my new song.its going to be super spiderly!
[alymay the spiderbard leaves the room]
me:moving on.
plan b:we set up a bomb .i will let argthik the goblin here tell you what happens next.
argthik:Building will go up in flames after making a nice big boom. Me want to see big boom. Me want to see a big boom make building on fire!
me:Yes yes now get back to work.
[captaindeath enters the room]
koboldcaptaindeath:What about sending in a small group of highly trained minions in order to assassin are target.[a map of a long detailed plan is rolled out]
captaindeath:as you can see here if everything goes to plan they should be able to get in and out before any one knows are target is dead.
me:We will put it under the maybe pile.
plan c: poison his drink.use strong poison in order to kill him fast. less powerful poison if you want to make him die nice and slow.
plan d:send him a gift. yes a gift. that once open will trap him in hell.nice and easy to pull off. a few things that can go wrong with the plan. the one who is to give him the gift could open it there self or does a half ass job by leaving it on his deck.Where any one could open it.
plan e:wait for 2012 when your new undead overlords take over.
plan f:start up what will form here on out be named the mob of gaming.then try to buy Activision. any one who is stoping you form buying Activision gets to have a nice *talk* with your minions in to why they should let you buy out Activision.
plan g:make up a new plan if all other plans fail.

For once I agree with you, kiddo.

Here's my question...does this mean a 100% shift towards a subscription model? If so, that actually might make more sense than releasing a full retail game every year (depending on monthly cost, of course).

We should just put him in North Korea.

Initially the MMO would be sold alongside normal games. It would only replace them entirely if its profitability rises to the point where it is making more money for far less work.
As with WoW and the like you would also see a stream of additional content released at regular intervals (piecemeal DLC and/or full expansions).
If you are buying every expansion that comes out in addition to paying for a subscription an MMO is far more expensive than buying each yearly instalment of a series.

It's times like this I'm quite happy that Activision hasn't made a single thing I've wanted to play in years.

Anyone read the interview he did on another site? Where he mentions that at Activision developers are treated as separate entities and they have control over their work, unlike at other companies. Either he's delusional or he's just a lying sack of shit. But either case, it doesnt matter really, he's only earning more money to the shareholders. And getting a big pay in the while.
...and, anyone know what were the sales of those map packs for MW2?

Just because you want to make money does not mean you have to try to ripoff your customers as much as possible. If you are slaves to shareholders then your weak and you need to grow a spin and tell them how things will be. He is an manipulative liar and I hope he will fail one day.

There is only one thing with the subscription model... WoW had and still has a community behind it. 99% of Activision's games don't have one bit of WoW's community.

I can't see why anyone would want a Call of Duty community. Like in game chat isn't bad enough.