Surely power available is merely a function of the weight of the batteries carried? Appreciate if you're going for ultra long endurance flying this might be an issue but the reality of a few hours airborne isn't that 8 HR epic power requirement?
I do also appreciate that such things cost money, and (particularly at the glider end of the market) a lot of people are right up against what they can afford as a hobby. However, for example, in a similar way to other mandated bits of kit (appreciate new radios were less expensive) given plenty of notice (say a 2025 cutoff) then most people should be able to afford the investment.
Where UAVs stand in all of this, buggered if I know. I genuinely don't think there's a practical solution to the risk of mil low flying having a mid air with a UAV. The only practical solution I can see is to make commercial operations notam'd and make mil aircraft sufficiently robust that a collision with anything sub-commercial is unlikely to be catastrophic.