Mistakes can be avoided totally locally,
Initially I thought the OP suggestion was bad, but now I think it is good with your comment. This is exactly the reason for us to make it non-standard. Since bitcoind won't broadcast non-standard transactions, we could avoid it locally by making them non-standard
its preferable to do things locally because it doesn't constrain what other people can do.
Agreed. We may have separate non-standard criteria: one for broadcasting, one for relaying, one for mining. Most of the time the rules are the same, but we may prohibit the broadcast of some transactions, such as having >0.1BTC miners fee. The rest of the network would still relay and mine these transactions