I've seen a lot of people complain that they don't like blast when they're just trying to mine a single block, and I have had that happen a few times, as I lost a valuable shulker because of that. I think /blast off or /blast on would be useful, so you could toggle the Blast enchant. EDIT:: I'm not sure how easily this would be to implement, but it's still an idea.
Tbh it's not that hard to add but I myself just have a 2nd pick in my inv at all times. Cool idea but I only see it being added if enough ppl request it.
I like this idea. I don't think people use shift much when using blast, so this would probably work pretty well. My other idea on how to implement would be a command to toggle it, similar to how ULTs use /enchant to add and remove silk touch from picks as needed.