I think if the parts were cheap and no special engineering was required, there would be a lot more people doing conversions. (And a lot of local shops that would do it for you if you paid them.) New EVs might outnumber converted EVs 100:1, but even that would be huge. Right now hardly anyone does it because it's super hard and pretty expensive. It just doesn't make financial sense.

(I'm currently in the process of converting a Mazda RX-8, using a Netgain Hyper9 in place of the original engine with the transmission kept as-is, and about 400 pounds or so of lithium iron phosphate batteries.)