I have raised a few Appaloosas with one registered Arab parent, and I have at least one due this spring. (I bred 2 reg. Arabian mares to my reg. Appaloosa stallion, and I am sure one is still carrying, but not so sure on the other-- she was checked in foal early on, but hasn't looked as pregnant as the other mares for the last month or so....)
I really like the potential of the cross-- both for type, and for the registration options with both ApHC and as a Half Arabian with AHA.
Far from being anything "new", it is a classic old cross which was recommended and used to build the early Appaloosa-- and by that I mean the Appaloosa which the ApHC developed and provides registration for.
Today it is not very common breeding at all in registered Appaloosas-- in fact for the last few years only around 30 Appaloosas with an Arabian parent were registered each year with the ApHC (less than 1% of the total Appaloosas registered with ApHC each year.)