Put me down for saying no middle ground is possible. If you have new print product coming out at any rate higher than zero, you WILL have the wall of books. The only dial you're controlling is how long it takes to get there. It FEELS like it took 3.x a bit longer to get there than Pathfinder, but regardless, they both got there. So did 4E. So, I will say this for the current release paradigm: those slim adventure books will hopefully keep the wall of books a little bit lighter when we eventually get there.
+1 to this.
Eventually, there will be a wall of books. It may take several years to get to that point, but it will get there. I think some people want that wall now. I will say that I absolutely to NOT want that wall to be built any faster. The slower the wall of books is built, the longer the game will receive support and remain the current version.
I look at it like this. If you had a game with a limited amount of high quality and useful books that can be produced for it, and you release them all right away, then what do you have to release later? A 5.5 edition, to start the cycle again? I don't think many people are clamoring for that.
Alternately, they could release all of the "quality" books near the beginning, then start to churn out useless books just to "keep 'em coming". I don't see that as a good thing either.
I think WotC are doing the right thing by releasing less books, especially rulebooks/splat books/etc.
I do think that there has been PLENTY of support for the game, thus far. It allows players to actually use the stuff that is coming out, and allows for WotC to take their time to do well thought out and high quality books.
Even if WotC only release two APs a year, and nothing more, then eventually a wall of books will happen. It will just take several years. I am 100% on board with that strategy. It keeps the 3 core books as evergreen and reduces confusion & the feeling of being overwhelmed by a mountain of rules, for the new players that come in.
There have been a lot of discussions on this forum in regards to attracting new players. Keeping it as simple/minimalist as possible is IMO the best way to go about it.
I wanted to play D&D for YEARS now, but never did, due to the wall of books the other editions produced. I didn't know where to start, and I wasn't about to start buying a wall of expensive books in the hope that I eventually figured it out. When I did get introduced to RPGs by an old school player (who was DMing PF) I was at a crossroads (so-to-speak), Start buying into PF, being way behind, and having a lot of rule books to pick up, or buy into 5E where I had exactly 3 books to buy in order to run the game. Future RPG players will have the same decision to face. Keeping the 3 core as the "evergreen" rule books make the choice easy and obvious. 5E will win.
Rules bloat = VERY bad IMO. Slow pace = Very good IMO.
IMO, YMMV, Etc.