I want to think that GTS isn't a demo, but more comparable to a prototype of sorts. Like comparing a concept car to its test mule, or its pre-production test type version, with a more "formal" GT game being the retail production model. Mostly something that's being used for PD to test a few things and gather the appropriate, relevant data. Stuff like using GT as an eSports platform, as a live service game, as the first game that doesn't have to be developed with the PS3's reportedly cumbersome cell processor, as a game that has direct influence on an actual car's design (the GR Supra), and building a sizable wave of partnerships (FIA, Michelin, TAG-Heuer, Toyota, Porsche) while building on pre-existing ones like the VGT project.
And I think for all the shortcomings GTS has, we don't know what workforce is being assigned to what on PD's end. I'd imagine that the reason there's still very sparse lobby options (especially compared to GT6) is in a large part because of GTS' focus on being an eSports platform, and so, many of the more notable gameplay/UI/UX/QoL adjustments and changes that we may want may be getting worked on for GT7 instead.
I think GT7 has a lot of potential, especially with all the expansions at PD, and the new partnerships that I think should help either improve GT as a game (Michelin and their tire simulation model) or financially, by helping to sponsor the game's production and events (TAG-Heuer, Red Bull). But I just hope GT7 isn't just a fancy tech demo to dazzle tech investors while leaving some stuff to be desired as an actual game. I get that ray-tracing, procedural generation of trees/buildings, the scapes, etc. are all indeed very impressive, but I hope that's all attached to a game that's also been able to evolve its actual gameplay and game design. For example, it could be neat to have different scoring or qualifying systems outside of the FIAGTC World Tour events, with options to customize them in lobbies. Or if there were abilities to create teams or clubs, and/or share liveries with specific individuals, or share settings in-game as you would a livery. And for the love of god, scrapping that god-awful exp/level system that has no place in a game where it's entirely unnecessary to have such shorthand for the actual firsthand experience you can gain on the track. Gran Turismo is not Dragon Quest, as much as I enjoy both. (Funny enough, I consider DR to be a decent enough replacement for the functions and purpose otherwise served by an exp/level system.)
I fully believe that the adage "beauty is only skin-deep" also applies to various products and entertainment; I don't want GT7 to have this paradox where it has tons of polish and yet nothing to actually polish.