I see no reason to '‘hack the grid driver’" to emulate the grid in norns.
its simpler to just write a matron “osc” driver that is able to send/receive grid events, its not that difficult to do, and is more flexible.
Im also not convinced of hacking scripts to support other devices, I think most want to be able to use existing scripts, and its also quite a lot of effort to start changing scripts like mlr which are not that simple - also then if/when that script gets updated, if your not careful you have to repeat the work again - imho, its not a sustainable approach.
screen mirroring - this is a bit trickier over osc, just because of the volume of data involved.
there would be two approaches:
a) send the underlying cairo calls as osc messages, (e.g. drawing lines, clear screen etc)
there would be quite a lot of (small) osc messages being sent, and it requires quite a bit processing on the tablet (which depending on what your using there might be easy or hard)
b) send ‘regular’ screen buffers
so let cairo process the messages then send back a screen buffer,
this makes the client side fairly ‘dumb’ / easy, but means quite a bit of data being transferred.
though admittedly the norns screen is pretty low resolution, so its not that much data.
Id probably try (b) first (as its quick and easy) , and see what the performance is like, before venturing into (a)
if your doing norns emulation, you’ll also need to do encoder/button emulation - but I think that’s already being done ( see above posts)
anyway, an ipad front end could be interesting 