Earlier today, someone decided to post to the Android issue tracker complaining about the lack of multiuser support for smartphones. Within a few hours, a developer at Google responded and closed the issue, remarking that "the development team has implemented this feature and it will be available as a part of the next public build." Sounds pretty definitive to us.
On tablets, the use case for multiple accounts (of course, Android has always been multiuser) is clear. The device is often shared among family members, so each user having her or his own account is very useful. For smartphones, though, this feature seems more for business use cases than for home user, where most people will have their own phone.
Pretty sure business users are going to love this: one device, two accounts. One for work, one for play.