Now these are actually some tough questions…
I assume that the controllers who have it are able to send a mix of 7-bit and 14-bit (often moving the 14-bit ones to NRPNs), I think that it would be within that same standard to continue from CC number 64 on to 95 (which is what I did with my controller), or even to just pick any CCs that are 32 numbers apart, and “14-bit mode” sounds like a proper name to me 
But it seems like there’s actually not much 14-bit controlling going on in the real world and not many controllers that support it.
Nonetheless I think it might be really good for Rack, since many modules have controls that would benefit from high resolution control and could easily be recreated as controllers with an arduino or some MIDI-board. Not many people will be able to use it, but probably more in the Rack community than anywhere else…
I will google some more, and if I find definitive answers to these questions I will post them.