Don't forget though that proper Dual Sports are a very small, niche market and not one that volume manufacturers would be much interested in for sales (prestige maybe, but not direct sales).
GS's are sold to people that want a tourer but don't want a 'tourer' (eg RT or similar). They may have once been bought by people that wanted an off road capable bike but that's long gone. That's not to say that some people don't take them off road of course..................
The 1190R though is, I think, quite unique in so much as it is actually a good off road bike (as opposed to just capable), has blistering on road performance and handling and will do a two up tour, not as well as a GS, but more than adequately. That said, it still appeals (in this country) to people who want it solely or mainly for the road (myself included).
The 1290 is a tourer, in the same mould as the GS Adv. Better in some respects, less good in others but on balance very similar.
So, what I'm babbling on about is I'd be surprised if bikes like these will get any smaller as they are sold as tourers, not Dual Sports. Any reference to Dual Sport is purely in the Marketing Departments hyperbole. The only exception is, maybe, the 1190R but even that is bought by people that want a tourer that can off road as much for the image as the reality.
Anyway, just to prove that any bike can go anywhere and that it's all a matter of attitude here's the same lane, a couple of years apart. The KTM is obviously far superior as it's on road tyres, the GS was on TKCs
Oh, and BTW Nutty...........whilst fire tracks, gravel tracks are great fun on a bike they are NOT 'off road'. An R1 could tackle a fire track quite successfully

Come up to the Peaks this winter for some proper muddy fun
Andres