I don't think you need any special GUI for that. It's just more how the software handles it. In MLCad, all buffer exchanged parts are shown to the user in editor mode. When you use a lot of buffer exchange, the model becomes quite a mess with all kinds of random parts (and arrows) everywhere.
It would be much easier if the editor itself had support for buffer exchange. That it really only shows what you would see in the step you're working on. If you know what I mean, my explanation is maybe a bit vague...
Aside from that, the 'current' buffer exchange is somehwat limited. I've had some annoying experiences with it in the past because it works not very intuitive (although that might also have to do with MLCad, I can't work very well with MLCad) and it's missing some features I'd really like. But, I suppose this is not the place to develop a new syntax
It would be much easier if the editor itself had support for buffer exchange. That it really only shows what you would see in the step you're working on. If you know what I mean, my explanation is maybe a bit vague...
Aside from that, the 'current' buffer exchange is somehwat limited. I've had some annoying experiences with it in the past because it works not very intuitive (although that might also have to do with MLCad, I can't work very well with MLCad) and it's missing some features I'd really like. But, I suppose this is not the place to develop a new syntax