With the change to weapon slots in the upcoming Forsaken DLC, lmgs could be viable since they could be put in any slot. I never used them in D1 (on my Xbox account) but if i could use a heavy machine gun, rocket launcher and sniper i think that would be pretty nifty. They should atleast be considered, an lmg would fit perfectly into the game when the weapon slots change.
I think the reason they were removed in the first place is because of their position as PvP heavy weapons. They objectively dominated the playing field and were deemed too odd to balance alongside rockets and were abandoned in favor of GLs, so I don't see them returning in D2. If anything they'll probably add one or two more sweet business-like LMG auto rifles.