My goal, and the entire reason for this discussion, is stil the same. I want to be able to connect a non-SKY box (i.e. a box running OpenPLi) to such a system, and be able to watch TV. At least all Freesat channels. Irrespective of the type of system my flat was configured for.
Yes and that would be the goal of any sensible designer of a new system... except Sky.
In the UK changing to the Sky Q LNB means no other equipment can be used. Just another way to make it more difficult for subscribers to drop the service and just plug in a generic satellite receiver.