If it's so trivial to implement then where is your proposed implementation and BIP? It could be re-implemented fifty times through rejections and objections and still be less work that the true work associated with all the testing, wallet implementations, and alt-implementations associated with this idea.
I was talking about from the wallet design perspective. Multi-sig & P2SH increases the complexity of the app. This change is trivial leverage in your software and dramatically simplifies it. I assure you I understand that any such changes are "not trivial" to implement in the protocol. But it certainly doesn't hurt that it's so simple in concept...