I remember the RJX/ARA being spoken about around the time ARA was started but the RJX never got a type certificate and support for what became a unique airframe would have been difficult. What would have been much more realistic would have been to make the ARA from one of the last RJ100 airframes.
Having spent so much time in G-LUXE, it's nice to see it being used fruitfully and the whole reason for BAe's proposal to FAAM in the late 1990s was to use airframe; otherwise it was being scrapped.