Rather than just copying other faction's basic repair mechanisms, why not add in cut content?
In Ardennes Assault, M3 Halftracks can be upgraded to toggle to repair nearby vehicles, basically a vehicle version of Ambulance. This can be an alternate utility upgrade for Ostheer (and/or Soviet?) halftracks; like the weapon upgrades, reinforcement (and transport?) is lost, but you gain a light vehicle that can run around healing friendly vehicles in a pinch. Pioniers will be a useful supplement in even the halftrack is lost or otherwise not yet available.
There is also the cut content of Ostheer's Forward HQ that spawns mechanics instead of medics, text description also claims it allowed forward retreat point. I've never seen this even in mods that feature the ability, though, it was just Soviet Forward HQ but mechanics instead of medics.
I was also thinking of a further repair speed at vet3, but the odds of Pioniers reaching that high and being retained just for repairs is rather slim; flamethrower Pioniers at vet3 are more useful when you keep them doing housecleaning.
Nice idea. The ostheer forward hq with repair was an abilty in a scrapped commander (the one with 5 man pzzgrens with flamers). It was doctrinal counterpart to the soviet forward hq, except you could also upgrade it to retreat point.
This is nice and cool but id rather have a non-doctrinal way of buffing up the repair speed. Repair kit upgrade or repairstation kinda seem like easier to do