they announced the race/class/diety unlocks come from achievements or quests, it didn't sound like paid unlocks will be an option.
The 1 character thing is a bit odd but they also said you can have alias's for your builds so multiple names is a thing even on one character and with all the unlocks available I guess the biggest thing you lose is bank mules, which don't really seem needed either, and the ability to reset and start from 0 since even if you reset your combos to a new race and delevel to 10 you will still be way ahead of someone starting a completely new character.
If anything I could see this being a play to charge for the character slots themselves for the people who want them.