I hate the idea of Constitutional Carry. I love the idea of being able to carry in all 50 states, but that decision should be left to the individual states to decide.
I don't really see an issue against constitutional carry. The people that carry legally are generally no threat. The people that don't carry legally would carry either way. The biggest difference I see is that you'd have one less thing to charge criminals with. There are enough constitutional carry states to tell if this is a big deal or not. I think it could easily happen in Indiana. But there are too many high population blue states for it to be a federal law.
At the national level to get that would probably require some really crazy compromises. I think the reciprocity carrot they stuffed in the Bill Shumer & Manchin put together after Sandy Hook was an example where the only way we get something at the national level, is to give up a lot more.