If they have studs for ball fulcrums, the step up to full rollers is not a big deal, just cost. For BPE the ball studs make finacial sense. Now for performance enthusiasts, we want to choose our rocker style, ratio and manufacturer. Not an issue. For the studs the threads in the head are all 7/16" UNC with a choice of 3/8" or 7/16" for the adjuster nuts. 7/16" are a bit stronger and less prone to flex. When they eventually do start supply of heads to the aftermarket, the stud size should be an option.
I thought about the canted valve idea, but the plan is a factory replacement with upgrades.