The trick is going to be making the game worth a sub fee.
If they can do that, then MMO players EXPECT that sub fee to be $15 per month. At that point the legacy players are just getting a discount. This is no different than Founder pricing in Rift, which was a system by which players that pre-ordered the game could lock in preferential pricing for the lifetime of their subscription (it came out to something like a 20% discount over a year's sub).
Console players are always going to have a problem with this precisely because they tend NOT to be MMO players. Console games with online components don't have sub fees, they also don't have constant development except in the form of DLC (which, ding ding ding, you pay for).