At that time there was still the strict separation between Roland Japan and Italy-based Roland Europe. GW7 and 8 were arrangers from Japan, and they didn‘t use some samples which had obviously been developed by Roland Europe exclusively for their arrangers (E-80, BK series). BK-9 was the last instrument developed by Roland Europe, and it included this small selection of 22 SuperNatural instruments from the Jupiters and Integra.
I think Roland has always been afraid of including too many of their new sounds in the factory sounds of their instruments, probably a mistake. I owned the BK-9, and NO, they did NOT include many SRX sounds in the factory ROM, in fact almost none of the SRX 04, 06 and 10 (I analysed the tone list thoroughly). Then, they announced expansions for the BK-9 which never came.
There‘s also a problem with the sound processor regarding SuperNatural sounds, this might be the reason why they just included 22 of them. It‘s a common issue of the Integra, too: too many SN-A sounds simultaneously result in timing issues, the processor can‘t manage the workload, as there is physical modeling involved.

Roland is going through massive restructuring at the moment and until they define what their focus is, there will be nothing radically new, however I believe the way things are going, TOTL arrangers are pretty much dead, (Just like there Atelier organs) particularly as arranger sales in Europe are declining fast. (To the current and recent generations of players there is virtually nothing of any relevance in an arranger for them)

Bill