I had a crack at it again as promised. But this task remains unsolveable. We can have either border select, or dragging objects around. And i will not remove the ability to simple drag objects or selected elements around.
I could map the functionality to alt instead of b. But this conflcits with the way the border select tool is made. It is not meant to hold the key down and drag. But activates with one key press. And you need a hotkey in all cases. And in Blender it’s B. So we better stick to B instead of inventing yet another key combo that nobody knows.
The other suggestion, to map deselect to a mouse click, conflicts with undo. At least in Edit mode. Undo goes one step too much back then.
So sorry folks, the official keymap will not change here. But you can always do your needed customizations by yourself 