If Phase 5 would deliver the replacement keycaps from their crowdfunded campaign three years ago we'd be able to do these conversions without touching a real 64. I haven't given up hope -- the machinery and molds are being moved to a company that specializes in this kind of low-volume production.
Maybe with these we could finally build the Commodore 256 ;-)
That said, it's not like the C64 is rare. I'd be more concerned about someone doing this to an Altair or a Lisa...
At least, I hope they don't.
Plus if we are completely honest, a refurbished original would also have more longevity than one with a raspberry pi which will have an initial novelty factor but then quickly get forgotten about once the Pi becomes obsolete.