I do think there is something to the barrier to entry argument, but it really depends on the army in question more than anything. Starting Empire of Vampires from scratch is going to cost more than Ogres or Warriors just based on the number of models you need. That being said, the internet is the great price equalizer.
The other thing is that fantasy does work as a skirmish game. And while a supplement to do something like that could be very nice and complimentary, playing fantasy at any level between 1000-2000 works. Generally speaking, percentages make it very good at lower points levels. The only thing that really changes as you move up is magic gets bigger/crazier.
I just think it's funny given that everything GW has done to increase the size of games through points reductions and supplements like storm of magic and we are talking about the need to make a skirmish game.
In terms of compendiums if you swapped lizards with wood elves in Order, swapped Skaven with Khemri in darkness, and put wood elves with ogres, khemri and maybe O&G in a nonaligned forces book it could work while largely respecting the fluff. But that still fails to address the balance issues that would obviously crop up from allowing elves to take empire artillery or vampire lords teaming up with just about anything else.
There is definitely something to the pop culture argument, but I think that game of thrones can be used as a guide post for where fantasy as a genre needs to go to be successful.