So what's the deal with these? forgive my ignorance. Briefly looking around, it looks like they're rare, compact BS?
CPTbadass has a lot of good links, but there's a few reasons these are wanted.
You know how aluminium cased cherry keyboards are often expensive? These have metal cases. Even the small 62 key weighs more than a full size model M. It's also got capacitive buckling spring (model F) technology and therefore NKRO. Finally, it's in a small 60% layout (very popular right now).
I would also like to note that it's got a very compact keyset, with a split shift and spacebar. It has extra keys instead of gaps in the bottom row (perfect for super or function keys between ctrl and alt) Also, I haven't tried it, but it looks like it might support a split backspace and right shift, so if you removed the two outer keys on the bottom row (and added some largerkeys and stabilizers for rightshift, enter, etc), you could have a HHKB layout model F.
All of this should be possible with a replacement controller, and possibly some extra keycaps, stabilizers and maybe an added hammer/spring or two (depending on layout)
The controller is not yet done. If you get one, you can start thinking about keycaps, layouts and modding (A replacement mat is a good place to start) until work on the controller is complete.
A lot of people have two qualms about the model F's They are large and have odd layouts. This solves both issues somewhat as it's smaller and supports a good variety of useful layouts. Added to that, it has a nice robust metal chassis
Until I get one, I can't say with certainty which of those split keys can be converted into a larger version, but I suspect enter and shift can. There is also an excellent chance you can put an ISO enter on there though I can't know for sure until I do it.