Even the 1918 BAR is a WW1 machine gun, and I could never see DF dropping them to level one, hell, I can’t even get them to drop the worst of the BAR’s to level two. 
But IMOP, the Madsen, Vickers and Bren all suck at level two. The German Mod30 is not terrible, but is bad compared to the MG13.
DF in the two years I have made suggestions has never listened to me, but if it were up to me this is what I would do if I were going to drop some MG’s to level one.
Allies: Vickers and Bren MK1 to level one. BAR 1918 to level two
Germans: Mod30 to level one
Soviets: Madsen to level one. BP RPK 1943 gets a 20 round mag and moved to level two tech tree.
Japan: Type 11 LMG to level one. Hotchkiss MG from BP to level two tech tree. If you haven’t tried out the Hotchkiss, I suggest trying it out. It uses a clip instead of a mag, and the clip looks gay, but it shoots smooth.