As we're just tossing around ideas:
"Morphing" (As on the Clavia / Nord synths): You select an input, channel, CC, you can set how much and in which direction it modulates any other CC on any output, allowing for very complex modulations at the touch of only one control. Ideally with modifiers etc. LFOs and Envelopes generated by the router itself as sources would be awesome, too!
Support for microtonal scales would be interesting - I think Tubbutec's Microtune module might be a source of inspiration.
BPM to Pitchbend calculator: A function that automatically calculates a Pitch Bend value to offset the tuning of loops in relationship to the actual BPM. Imagine you have some sampled percussion loops that are at 125 BPM, and you are playing at 128. You can enter both the original BPM of your loops and how many semitones your sampler detunes them in reaction to Pitch Bend. The router then calculates the needed PB value to send to the sampler patch so the loops are at the correct pitch (well, length, rather...). Something like :128/125=1.024, sampler pitchbends sounds 7 semitones, so PB value needed = XXXX
A "performance mode", with split zones etc, both for keyboards and controllers.
CC/NRPN/SYSEX presets for all kind of gear (can be added and exchanged by the community). So if someone figures out the Juno-106 SYSEX implementation, he can easily share it with all other users. Built in CC to NRPN/SYSEX (or even other CCs to standardize your implementation) conversion makes light work of automating such synths. This would even allow your controllers / sequencers permanently sending the same 16 or so CCs, and the conversion just takes place in the router. Pretty handy if you'd know that Parameter Layer 9, permanently assigned to CC12 on the MBSEQ is always changing Filter Env amount on all your synths. That would also be great to swap out different synths without having to change the assignments in the sequences!
Editing of the CC to CC/NRPN/SYSEX conversion presets would be best in some kind of list editor (on a computer), vertical row shows incoming CCs, horizontal rows are all your synths. Now you can just select the function you want controlled in a cell via a drop down box.
Man, I never thought that thinking about a MIDI router could get me excited ...