People will just rushtech T2 and then blob with your Panzerjagers idea. 290MP isn't a huge cost to 4-man squad, especially if you got like one Volksgrenadier squad nearby to pick up dropped panzerschrecks.
It might fix volksblob, but the result is creating a different blob. It may be even worse as you no longer need T1 queue to get Kubels, trucks and Sturms, you have a separate T2 queue for AT blobs. For better results, you train a mix of PJs and Volks and blob your way to victory.
As for becoming more like Ostheer, it shouldn't be embraced.
In any case few people will bother with a MP40 upgrade, they'll keep the slots and munitions for re-equipping panzerschrecks and dropped LMGs, etc.
Not really.
Because the spam of units that only have AT units will lead to trouble with OKW, especially considering how strong allied infantry is.
That and considering how panzjerjager squads as proposed start with AT rifles and you still have to upgrade schrecks, you wouldn't necessary have a volksquad to tag along.
MP40 upgrade is designed to be situational. It can help in certain situations and certain maps just like in VCoH. It's not like the LMG42 upgrade which is always good.