Arca-Swiss is better at future-proofing for the moment, they have more capacity to do things like focal plane shutters and their own electronic shutters than Cambo seems to have, but personally I would not worry about that. It will be many years before we see the end of Copals even if not any new are made, and by then I guess Cambo and even Linhof will have come up with a shutter solution.
For a pancake cam I think high precision focusing is a must, being able to set an exact focus distance direct on the focusing ring without looking is a prime feature and is very useful in architecture. With RM3Di you can do that, with Cambo you need Alpa HPF rings, be sure to check out if so there are no caveats there. Actually, I think Alpa has the best precision/speed tradeoff, RM3Di is a bit overkill precision in that regard, but if you think it's fast enough to turn then it's okay.
With the new Canon TS-Es you can tilt diagonally. That's not possible with the Arca, but it is with Cambo tilt mounts. In architecture I doubt you will miss diagonal tilts though.
If cost is an issue, you could look into getting a Hasselblad CFV-50 (if you can find one) and work with Schneider Digitar wide angles instead of Rodenstock. With that a bit smaller sensor size (49x37mm) you'll experience larger movement range relatively seen which I know I appreciate. But an IQ160 with Rodenstock Digaron-W 32 will be higher end than CFV-50 with Schneider Digitar 28, but also a much higher cost system. The Linhof Techno as suggested above will lower the cost of the system when you have a few lenses as lens mounts are only the cost of a lens board. But sliding back and ground glass is not for everyone. I have a Linhof Techno myself, but I shoot landscape, if I would shoot primarily architecture I would probably go for an Arca-Swiss or Alpa system (some pros still use Linhof Techno for architecture, tastes are different). F-Universalis is also a view camera, ie focus with live view or ground glass.