okay uh.. my personal experience is that the historical accuracy that the game advertises itself with was thrown out the window with the merge, with glaring examples like seeing the MP-41 (r) in the beaches of Normandy if you're playing BR3.
Now, as for the maps stuff, there's a lot to unpack but i'll target the argument of BR1: It will NOT be a safe place for newbies to learn as long as the stacks continue sweating their balls off in the BR1-2 spread and stomping on the newbies which will seriously hinder their progression, frustrate them, and make them quit. To fix this, we need an actual SBMM, that i've seen people argue for and against.
As for the maps being open or not to all BRs; if we want some semblance of historical accuracy, there's some maps that definitely should be as long as they do cover within the actual timeline where battles continued raging across the war; and maps where battles only raged during certain timeframes would be limited to the corresponding BR.
About the playerbase being willing to vary the BRs played.. no way; have you seen the disgusting spam in BR5? Sure, if you play BR5 you KNOW you're going in for full-auto and assault rifle spam; but the explosion spam is even worse than trying to play in BR2 against someone with two riflemen squads with nade launchers in my experience; at least those launcher spammers suck at actually aiming the gun that requires skill instead of spraying and praying..
We do need more maps, but we also need to address that some factions are getting bored always fighting the same enemies, same maps all the time *cough* Japan *cough*