Great! Thanks for your confirmation on my observations regarding the Nordic SoftDevice and the Zephyr implementation.
I think for a BLE host (central role) implementation we will forward for the 2 boards solutions, running on the BLE host board a Linux OS that uses a BLE SW framework (e.g. QT BLE) that is BlueZ based and using the Nordic HW board as connectivity chip, the BLE controller based on Zephyr.
Nevertheless if Nordic's PC BLE driver SW stack becomes more mature and stable it might also be a solution.
However my experience with running Zephyr on the Nordic nRF52 is so far great, so it will be hard to move back to the "serialization solution" of Nordic that is also nice.