I just had a little idea, and I think it could be implemented without too much work (perhaps as a script, or plugin) by someone more skilled than myself...
Consider this:
Many people like having a vanity address, but using it within electrum means having to import it, which is not cool as it somewhat defeats the purpose of a deterministic wallet. So how about writing a function that takes the vanity privkey as input and derives an regular electrum seed which has this vanity key as the first 'receive' key of the deterministic sequence?
Seems to me this would combine the benefits of both vanity and deterministic addresses and wouldn't compromise the security/randomness of the seed in a significant way at all. But I could be wrong. Thoughts?
It would work but would run so slowly as to be impractical for generating anything but short vanities.
I'll rephrase this: you actually can't take an arbitrary privkey that wasn't derived from a seed, and come up with a seed that can be used to derive it. Since that's impossible, I have assumed you're simply asking about the broader case, "can I come up with a seed that generates, among other keys, an address with the prefix of my choice".
Current vanity generators depend on being able to exploit the speed gain derived from using an EC add rather than EC multiply. Anything that takes away that improvement is going to throw performance back to the stone age. Anything that includes derivation from a seed must be followed by an EC multiply to become a bitcoin address and therefore is an example of it.
