Every non-sphere class can become close to a half-sphere class by sacrificing half of their feats earned by character advancement for a 'Proficient' Talent point gain. It's more feat efficient than the Extra Combat Talent feat, but is more of a commitment too. And of course, you can multi-class into a Sphere class, as I intend to do next level, though, it's a bit tricky, as if you want to grab the martial tradition for a Sphere Package, you have to have proficiency in all martial weapons, or a exotic one, and forego the proficiencies you have gained from your original class in favour of the martial tradition. I think the Sphere classes were made worse to multiclass with so you couldn't just grab each of their martial classes for their strong 1st level abilities and proficiencies.