Well not much more modern unless you use the expensive manganese steel from the FG42, or chrome lining as the RPK. You are basically talking about a value engineered Colt Monitor.
It really adds nothing. As Derwint said everyones WW2 kit derives from WW1 experience. There is nothing in Germanies ww1 experience calling for an automatic rifle and certainly no economic reason to develop a second MG series. When they come around to rearmament a tripod MG with a bipod version is a cheap logical extension ( in terms of manufacturing plant and ease of supply) which fits in well with German experience and doctrine from WW1. As it is the Germans are always struggling to have enough MG to issue and switched production from ZBZ to MG43 during the war so they pretty much did not see the need.
The FG42 dropped the manganese steel after the initial model with the 60 degree pistol grip and gained weight for the main production model:
https://en.wikipedia.org/wiki/FG_42#Deployment
After approximately 2,000 FG 42s had been produced by Krieghoff, supplies of the
manganese steel from which the receivers were forged were diverted to other needs; this meant a redesign was required to use stamped sheet metal in its place. Field reports were also requesting minor improvements, such as: relocating the bipod from the front of the handguard to the muzzle to reduce shot dispersion; changing the pistol grip angle to near vertical; enlarging the handguard and changing the stock from stamped steel to wood to minimize overheating. These changes, particularly the pistol grip change and the bipod relocation, are clearly visible on late-model FG 42s. Both models also had a simple flip-out spike bayonet under the barrel hidden by the bipod. In the later version the bayonet was shortened from around 10 inches (250 mm) to around 6 inches (150 mm).
Chroming barrels was something all sides were doing in WW2, but even the non-chromed barrels of the MG42 could handle several hundred rounds before needing to be switched out and that was at a very high rate of fire, which shortened the time between changeouts more than the same number of rounds from a low rate of fire weapon. Supposedly the Bren gunners didn't bother changing barrels, because the weapon didn't heat up quickly enough to make it necessary due to having a 500 rpm ROF.
Having two automatic rifles instead of one belt fed weapon adds nothing? Having a weapon that could keep up with the advance and allow for mutually supporting fire teams doesn't change a thing? In terms of cost the machined MG34 was not cheap and had to be replaced with the MG42; even that was due to be replaced by the MG45 that was much simplified and lighter, but the war ended before it could be produced. Having a light stamped steel automatic rifle would be a lot less expensive. The ZB26 for instance was cheaper to make than the MG34 and IIRC even the MG42.
The switch from the ZB machine guns to the MG34 was a choice made so that there was a supply of MG34s for vehicle defensive gun mounts, as the MG42 couldn't fit in those, while the MG34 production in Germany was getting switched to MG42. The ZB series was phased out because they wanted to standardize production, not because it was a poor weapon or appreciably worse than anything else fielded.
The GPMG/Universal MG was more a function of Germany's production staff deciding to try and boost production by having a single model to make, but they screwed that up by having a design that was effectively only made by machined parts by master craftsmen, which led to it being replaced by the largely stamped MG42. In the interwar period the design was fine given how small the German army was and how long it needed to make equipment last. For scaleable production in wartime when weapon life might be considerably shorter it was a flawed choice to ended up being replaced.
Leaving aside the WW1 experience argument, let's say for the sake of argument Germany realizes it could use a cheap stamped metal autorifle like the French did in WW1 and manage just fine with the modernized Dreyse MG as a HMG for company and battalion use. If we really need a POD let's say the BAR makes it to the battlefield in WW1 and makes enough of an impression that the Germans opt to copy the concept and improve on it.