The only difference between the current BG system and and advance reservation system, is all of the sad people who could not get reservations would be tucked out of sight at home, instead of being where Disney could any least try to cheer them up. Also advanced reservations would greatly open the system to being hacked so that some people would always get boarding groups.
If anything the current system is better because at least only people who make the effort to get into
Disneyland/DHS before opening are able to try. With everyone on Earth able to try remotely? No thanks!
The only system that is actually FAIR mind you, is where people who get in line early are the first one to get a boarding group. I've gone to ROTR under both systems now, and the first come first serve system was by the far the one that was most fair and produced fewer unhappy people. You could know on the way if you had a shot, or by looking at lines to get in. Now it's just everyone who can cram into the park by 8am and then a battle royale of phone technology skills to determine the winner.
Now mind you, I'm not sure at this point if the more actually fair system is better. I think what Disney is doing now, is probably the best compromise (but then being good with phones I can rationalize that since I"ve always managed to get a boarding pass so far).
They could do that without changing the current system. I think you are severely underestimating demand though, I doubt that would help much.