Yes that's what I meant. The block chain is still entirely self-validating if the transaction hash doesn't include the signature as long as you bother to store the signature. At the moment though you HAVE to store the signatures. Can anyone propose a remotely plausible scenario in which we would regret not hashing the signatures?
You don't have to store the signatures you have to store the signatures OR the txid, ultraprune stores the TXID but not the signatures in its coins database (which is the only thing it uses for validation, so not just possible, but implemented). Because maximally efficient pruning always instantly prunes the signatures and does pruning per txout instead of per transaction you're going to have to store the txid anyways.
This is why I was loudly beating the drum up-thread about saying any OP_DROP stuff, if it exists at all should be in the scriptsig, and not the scriptpubkey... scriptsigs are always instantly prunable.
Unless you were talking about the data you need to initialize another node that doesn't trust you completely, in which case you can't discard the signatures no matter what is hashed.