The 'flat' designs (Lithium Polymer) will be around, but I am not sure they'll be a 'standard'.
Because they are primarily for the handheld market, they are usually made for handset manufacturers - while that mfr wants them, they'll be around, but as soon as the mfr moves to a new case, that's it (been burned that way).
The move to flat packs is definitely under way, though. I figure it'll be a couple of years before we get a usable standard.
Cheers
PeteS