So the Twin & "Old School" machines continue to sell well and the "New Design" hardware needs a sales incentive? Again, the existing Himalayan can contain a 460cc displacement. It's EFI. Doesn't it make a lot more sense to boost its displacement literally for free than do a lot of R&D on another "New Design" machine?
If R.E. entered Paris-Dakar and competed with a Twin and a new 450 motor version (that has enough street legal copies to qualify: 200 or so hand-made copies?), AND the new engine machine did very well while the Twin finished at least mid-pack, they you might have some basis to pursue a truly new design. Racing does sell hardware, but it's not cheap advertising. I've never seen R.E. show any interest in moto-competition.
I think the Twin is a terrific effort. The Meteor as a 350 & also a 500 would just be business as usual for them. The Himalayan is an outlier; a very good effort, but not selling as well as the more traditional singles. Again, it would really puzzle me as to why R.E. would launch a second, virtually identical, "trail machine" modern single effort when they have no competition based advertising driven reason to do so.