How so?
If you went Battlegroup you wouldn't.
The point would be to give Mechanized cheaper access to Battlegroup medics. At the moment they've got to buy the truck, the building and the medic upgrade to do that. This would cut out the building cost.
Is that necessary at the moment? Probably not. Pre-DBP Mechanized was dominant over Battlegroup much like Battlegroup is now dominant over Mechanized. That tells me the tradeoff of relying on crates isn't a dealbreaker.
I agree that one can definitely play on crates only if they rush mechanised. Especially as these are most probably getting buffed in the new patch to cover up the bug.
On a side note, your idea doesn't actually add anything to mechanised build. Think of it. Right now if you want both fast mechanised unit (probably luchs) and base healing, you would go mechanised first, then you would build the luchs and go for the second truck with its upgrade. With your changes, you would have to go for mechanised, upgrade it to produce units, build luchs and then build second truck. That way you pay exactly the same, but you get the luchs later and you can't build units from battlegroup. The only advantage you get is the free repair upgrade, but that comes before any units you could repair, unless you go for multiple kubels. For most builds, single luchs and single kubel can be quickly repaired by sturmpios. Base repairs really becomes important only at medium tank level and up.