I saw photos a few months ago somewhere of a 650 Himalayan, a factory styling exercise I think. It just looked like continental GT with long legs, rather than a Himalayan with two exhausts. A beefier single cylinder Himalayan would be interesting.
I also think a bigger single (600cc?), for a wider range of road use would be interesting. CCM offer an interesting take on this in the UK. I reckon a retro Enfield style single could capture a wider market if it could sit comfortably at 80mph. Though I doubt it would be the sort of sales numbers Enfield India would need to be take interest. Someone needs to resurrect BSA, or a modern Ariel Red Hunter...?
I love my 500 though, but I need my second bike for when I'm out with mates.