I think It will be based on Debian testing version for what I've read or at least that is what I understand: fully fledged Debian-compliant packaging and repositories.
If so, all depends on the debian realeses (stable and testing). Wheezy is still the testing version, but about to migrate to the stable version.
It has been freezed up almost 4 moths ago and almost ready to become the stable release, in which case Sid (Jesse) version will be the testing version.
I really hope is totally based on Debian. If so, perhaps all timming might depends on Debian development and packaging migration.
The BT5 team is doing a titanic effort .
let's just wait, in the mean time, all comes down to speculations.