There are a couple of good options for working with truncated blockchains to a checkpoint without reducing the security of the blockchain. Likely one or the oth

There are a couple of good options for working with truncated blockchains to a checkpoint without reducing the security of the blockchain. Likely one or the other with settle out as the common practice, and the blockchain growth problem will be solved. Power consumption, on the other hand, may not be solvable even in theory, and it also seems likely to drive mining to just large service providers. The current pools aren't a solution in this case because the startup cost to even participate meaningfully will grow too large. Maybe this could be solvable with a different proof mechanism. A few have been suggested and tried (PPC etc.), but I don't think it's solvable for BTC as it's currently defined. I'm happy to be proven wrong.