In a way that's kind of what SuperNET is doing.
Also, there is the Jay framework: http://jnxt.org/jay/
Thanks, I didn't know Jay. If it is safe/stable enough for merchants, it can be a good solution for them.
SuperNET is a bit off my radar and it surprises me that you mention it, as I thought it was a pretty heavy solution. Must take a read about it.
Anyway, I would really like to see a minimalistic Nxt command line client with only the core features
I would stay away from Supernet. It has like 25 parts and 20 of them are vaporware, and of the 5 that do work, none particularly work well.
But there is solid development going on within the NXT core.