On a positive note, here in England image2output offer fantastic knowledge and support along with rapid turn around times for repairs/servicing/supply of all parts for our Sinar P3 system.
It differs from one place to another depending on the interest of service technicians to specialize with a certain maker or work independent... Certainly the best of technicians avoid to be certified by one maker only as the demands of makers as to get the authorization is with all makers insane... Certainly Leica is no worst than the rest of the makers in this respect...
I would love to see a new Sinar Hy6 type camera - this would give us the opportunity to work both with a fixed P3 and handheld during the same shoot, without the hassle of matching colour between Sinar and other manufacturers systems.
My guess is that this won't happen... Leica S works with the same software and calibration method as Sinarbacks do and thus they do have a solution for the requirement you set... What would make sense though, is for them to have the sensors replaced on their Sinarbacks as to be of the same origin as the Leica S 007 sensor, as it would both improve compatibility further and would improve company image as to be one of using "exclusive to the maker" sensors...
IMO, Leica aims to have the "digital part" (sensors, software, interface) under the Leica name and then the mechanical part for "special pro applications" to Sinar... IMO, the SL is mainly aimed to replace Sinarbacks on the rear standards of Sinars and then link the Sinar system to the Leica S one... I won't be surprised at all if Leica will have a multishot version of the SL released sometime in the near future either...
Thus, my first bet as far as Sinar products are concerned, would go for a dedicated Tech camera as to take full advantage of SL used instead of an MFDB on the rear standard of a view camera... (perhaps with Leica S lenses on the front standard's lens board?)