Well, not quite. The preproduction photos suggests that there's still a problem with the depth of the footplate drop, especially in front - Rapido seem to have used the shallow "N" one, thus repeating the mistake that DJH made on their new-build "U" kit. It would look wrong on a Woolwich K1a as well.
The "U" and K1a had a very deep and noticeable drop from footplate down to bufferbeam - it has rarely if ever been modelled correctly, mainly because modellers assumed it was the same as the original N/K1.
The K1a used the same chassis wheelbase as the K1, 7'3" x 8'3", unlike the "U" which is 6 inches shorter between driving and trailing axles.
The other thing is that Rapido don't really cater for the finescale gauges. Clearances have tended to be insufficient and Rapido engineering has been quite unlike everyone else's - it's almost as if they'd deliberately designed them not to be tampered with.
People have already had considerable problems trying to convert from OO to P4, and there would be even bigger problems going to 21mm, especially with the extra 2mm between the visible frames to be grafted in.
I have a Rapido USATC S160 on order for end of next year, and I'm expecting it to be a nightmare P4 conversion.