If future setting books mimic the format of SCAG, will you purchase them?
I will kick it off by saying no. I think this format is way to thin and lacking for my tastes. Forgotten Realms is a massively, rich world full of lore and this format does it no justice.
I think you're just protesting, and that you (and everybody else) will come round once it's apparent this is all we're gonna get.
Yes, I believe the time for 3E FRCS style books has passed.
Yes, I believe the time for Complete Fighter style books has passed.
WotC has simply decided it's too much effort for too little gain. Better to sell books that combine 10% of the fluff from an old-edition campaign guide with 10% of the crunch from an old-edition class splatbook, and sell that at 100% of the price.
Remember, WotC is far from going all-in on Dungeons & Dragons this time. To me, it's apparant Hasbro has instructed WotC to maintain a holding pattern, investing the minimal effort needed to keep the gamers reasonably happy to keep the brand afloat.
All the while, expanding D&D into movies and toys is where the real money is at.
I fully expect the next "adventurer's guide" to cover another region of Forgotten Realms, and to include a new smattering of crunch. Leaving the Realms for another campaign setting simply draws a smaller audience. If anything, it wouldn't surprise me if WotC were to add stuff previously exclusive to other campaign settings (such as Eberron) into that FR book.
So yes, I believe the time where WotC simultaneously provides active support for more than one setting has passed. It makes much more financial sense to target ALL gamers all the time, never delving into a niche.
SCAG fits this pattern. It appeals to players and dungeons masters alike. It offers bits of support for previous editions (such as bladesingers and warlords/purple knights). It adds crunchy bits you can use for your own campaign set in another world (such as Eberron, Dark Sun or what have you) without needlessly excluding the Realms fans.
So I vote "yes". But not only that, I wager you too will come around and vote yes, eventually.