You're correct in that it can't be put on a UC. I wouldn't mind the ability if that was still possible, but don't like having to build a AEC in a 4v4 just to use the ability.
The bonuses provided by the aura and the timing are simply to high to be available in UC.
Imo strong passive aura should simply not available. There are a number of solution that can included timed auras or creating a command vehicle instead of upgrading one.
If you blobbing but do not want to get an AEC you can upgrade:
A Centaur it will probably still be able to offer some AA and it Vet 1 ability would still be good AI.
A Cromwell. It will still be able to fire smoke and if the blob is big enough it will provide more DPS than you will lose
A Churchill or Croc. The main gun will not be great but again if the blob is big enough.
I understand why they limited the number of models on Infiltration commandoes when used as an infiltration units, but think they should get all of their models when not used as infiltration units.
Although I generally agree that infiltration units (that come with premium) should be able to be build from HQ without it the Command are in weird place since the might become superior to other Commandos available.
I guess one could redesign them to be 4 men commands armed with 4 Enfield (or 3+pistol or 2+2 De lisle) able to upgrade with brens.