I think this needs more details before it gets a BIP number; for example, which opcodes does this affect, and how, exactly, does it affect them? Is the merkle root in the block header computed using normalized transaction ids or normalized ids?
I think there might actually be two or three or four BIPs here:
+ Overall "what is trying to be accomplished"
+ Changes to the OP_*SIG* opcodes
+ Changes to the bloom-filtering SPV support
+ ...eventually, hard fork rollout plan
I also think that it is a good idea to have actually implemented a proposal before getting a BIP number. At least, I find that actually writing the code often turns up issues I hadn't considered when thinking about the problem at a high level. And I STRONGLY believe BIPs should be descriptive ("here is how this thing works") not proscriptive ("here's how I think we should all do it").
Finally: I like the idea of moving to a normalized txid. But it might make sense to bundle that change with a bigger change to OP_CHECKSIG; see Greg Maxwell's excellent talk about his current thoughts on that topic: