The Hy6 is not in any way limiting the adaption of a Sinarback: ANY Sinarback which can be mounted on a Hy6 can ALSO be mounted on a view camera (being it a Sinar one, or another), simply with the respective adapter plate.
I may be don't get your point, but it seems that there is confusion
IF YOU USE THIRD PARTY AND SOON TO BE DISCONTUINUED PRODUCTS..
If I am correct using a 6008 and suddenly needing wide you just drop the back off and plonk it on the the alpa with a 28 or 24 - no screws - click
Should you need rise on your R lenses with you just stick your 6008 lens on the alpa - click
Should you need movements you just drop you back into a Xact - no screw - same lenses - click click
Subject to image circle limitations this is the most flexible and economic system possible.
ON THE OTHER HAND
If you are loyal to sinars current and announced future products..
You are using a HY6 and suddenly need wide you
unscrew the mount and replace with a P3 mount, you have to use a P3 becuse sinar dont make a handy little camera like the Alpa
should you need movements you then go out and buy a SECOND set of LENSES for your view camera because you Hy6 /rollei lenses DONT fit on the view camera
we know those lenses have a coverage beyond 645 but there is no way to access it
Maybe I am confused.
I challenge you to a race - time is of course money to my clients.
We both photograph a hotel, detail shots and some wide shots with rise and fall and a few details with some rise too
I use a rollie 6008 and a 28 on an ALPA
You use a P3 and and HY6
Anyway I won for the first 10 hotels because you were still saving up for your second set of lenses