It's possible you're not properly distinguishing between alt-coins and what could be classified better as bitcoin blockchain forks. Maybe the design differences are mostly not very inspired, but some may have features that make them incompatible with the bitcoin keypair specification. The argument for alt-clones breaks down for a coin like that.
Your bitcoin key-pair is used exactly once to claim your æther. After the æther is claimed, the functionality is identical to Ethereum and you'd use ethereum key pairs from that point onwards. This is the only additional piece of code one would need to write: basically a transmission from bitcoin space to æther space.
I believe my proposal works for any possible alt coin. My proposal is simply a way to create a distribution of wealth equal to that of bitcoin in any new alt coin.