Are the metamagic feats specifically mentioned in the metamagic portion meant to be the only ones added to sphere effects? Notably rime spell isn't on there despite the fact that it could logically be applied to cold damage destructive blasts.
The metamagic feats section on the SoP wiki at least mentions the classic metamagic feats in its example and even explains how Quicken Spell is supposed to work, so I assume sphere abilities are supposed to work with already published metamagic feats.
They are revising it with the release of Ultimate Spheres of Power. Any Metamagic can be use except for Heighten Spell, so long as the effect could reasonably be affected by that metamagic. So Rime works just fine.
They're also getting a bunch of metamagic rods in an upcoming book, which have effects adjusted to work with spheres' talent-based system. It's not much of a stretch to take those effects and use them as a feat instead.