Ben I thought that when I saw the post originally. Probably not plated, and I wondered if not using it on the road till after the new regulations came in mattered. Wasn't sure how easy getting triggers broom through the new regs would be?
But when I studied the photos more it'd need:
2 sets of suspension units with hubs (2 x 75) and road wheels (4 x 35)
?jockey wheel may be easier than the current nose wheel (15)
lighting etc (15)
4 wheel arches (4 x 5)
Possibly a winch to reduce the need for dunking (30)
Would guess all that will be heavy which may mean it needs to be braked? (add maybe 150 per wheel set plus needs fancier hitches etc)
Back of a fag packet prices...c.£400 if unbraked, going up to more like £8-900 braked. Unless I've missed things?
Not sure what the rib is but you'd get a (new, fully legal) bunked trailer for 4.5m for <£1k and a braked roller for a heavier boat of similar size for about 50% more. Thats without really shopping around.
The snag with the launch trolley is that while there probably are people who might want it the reason they want a trolley and not a trailer is often in part cost! You need to never want to take your boat anywhere - which means its sailing clubs etc that want it and while they are all loaded with posh yachty types - they are all tight! Add to that the complication of getting it there...
My biggest reservation with converting it (other than weight) would be width - the side poles look very far out relative to the wheels...?