only the third one is. The other two are keytronic foam&foil.
The seller (cellarnow) recently sold a bunch of hall effect boards, so that's maybe why they popped up on your search?
As far as re-riveting the PCB, it depends on what sort of hall effect switch it is. the "dual magnet" style switches are riveted to the PCB, and the "single magnet" style switches are usually screwed down to the PCB (you can actually screw down each switch individually: there's a screw hole under all of them. Some have a standoff that's screwed down as well, like many cherry KBs with plates.
So with no modification to the PCB, you could very likely get a 2KRO (or possibly 4KRO) keyboard. All the switches' power are wired up in parallel, and the outputs are usually wired up normally. Since there are two outputs wired to two separate matricies, you might be able to get 4KRO, but it's just a guess for now.
If you desolder the PCB, cut all the traces, then resolder all the switches to it, you can do your direct-wiring scheme in a few different ways and get NKRO out of it.
re-soldering the switches (technically just the sensors) to the PCB just keeps them in place. then you direct wire to a controller of your choice "under" the PCB.
Making a custom PCB for your personal board is a great solution. You can even home-etch it. it solves a lot of problems.
about messing up the sensors: they're pretty tough. they are mounted to either a black plastic case with a window (dual magnet) or to a ceramic PCB (single magnet). Single magnet is much more common, and is the hall KB you have linked.
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The switches really last forever since there's no contact: nothing to wear out. That said, I have several boards that show evidence of switch replacement. They were sued in a very industrial setting though, which could explain it.
I also have a board with
significant wear on the stems that's not too great to type on. If you keep it maintained (just lube the stems every once-in-a-while, etc.) then you should be okay. after some care restoring it the heavily worn switches still type well. The KB is currently in pieces awaiting my further restoration.
One other thing to note: they're not always the best to actually use. There's not a lot of modifiers on the spacebar row. This can be fixed with some keyboards, but you can always cut a new hole for a switch in the case and put a new key location down. Especially if you are designing your own pcb for it.
oh: another thing. Signature plastics can make keycaps for these switches. I have no idea why, but I received several in the "crap bags" that I have tested and do fit fine. they're not as nice as genuine keycaps (well some of the later keycaps look almost identical, but the older ones are nicer for sure), but work perfectly, and are nice and thick (like SP's SA keycaps)
hope this helps!
Will they take this seriously?
Doubt it but it cant hurt to ask.
http://sensing.honeywell.com/index.php?ci_id=47847read some of the above paper on it: its more general: about all hall switches, not just for keyboards, but the beginning is a real wealth of information, it's where the 30 billion number came from.
