A caravan "MOT" would be a very limited affair, in my view.
With cars, which you really cannot use as a comparison, the extra items brought into the test over years are all to do with construction and use, vehicle mounting points, such as shock absorber mountings, and items wich will significantly affect the roadholding and safety of the occupants.
Caravans on the other hand have relatively few points to check regarding roadworthiness, wheels and bearings, body to chassis fixings and lights.
The idea of a test station being able to determine the effeciveness of a stabiliser is not something they could do, unless is just an inspection, as there is no requirement to have a stabiliser.
As for the jockey wheel, again , it is a non road contact piece of equipment which is only used for very limited purposes, mostly for levelling on site and of course moving the van off the tow vehicle.
Unless the rules change, which may happen, the gas system on a touring carvan, privately owned and not hired out as part of a business is exempt from CORGI regs, so just a gas leak test would be all that a test could legally consist of, but even that would be questionable as all the systems in a van are deemed as "plug in "systems which are not, or do not have to be, a permanent fitting.