Fair comment, Sidewinder.
And whilst there may still be some opportunities to get a few vehicles through the system by presenting well-reasoned cases on specific points, I guess we do have to be realistic about the future, and to that end here is how I see the process for registering post 1973 mvs going:
I imagine that DVLA will require an SVA for any vehicle which falls outside a fairly conventional category. This is the only sensible way they can ensure that only vehicles which comply in all respects with the relevant regulations do get registered. I don't think the argument of 'you've already registered some of this type, so why not mine?' will work, however unfair it may seem.
Try putting yourself in their shoes - how else could you do it?
Sadly I cannot see anyone going to the expense of obtaining Type Approval for any breed of unconventional mv.
I would hope that DVLA will not be unduly concerned with any non-compliant vehicles which may have already slipped through the net (for whatever reason), so hopefully those owners can continue to enjoy the priviledge of driving them on the public highway.