if I were a consumer contemplating a conversion, the following would be the only situations where it might make some sense:
1) you have a Recumbent trike you want to convert
2) you have an adult upright trike
3) you want to really hot rod a regular bike with more than 1000 watts and don't care about the legal ramifications
For regular bikes, it's hard to justify the time and the effort, and research it will take.
Just my two cents.
there are many things you can't buy in today's market. I wanted a bike that would 1 carry 80 lb cargo, 2 not throw me over the handlebars on my chin, 3 climb 15% grade without power @ 1.5 mph, 4 carry me back from 50 mile out concert excursions when I was tired, and 5 push me sitting straight up 30 miles into a 25 mph headwind at 9 mph.
Item 2 is nearly impossible. I examined 150 frames with 26" wheels and all had the same inadequate trail, or in automotive terms caster. Mother had a 1946 firestone bike that was stable with 26x2" wheels, but it was single speed coaster brake & weighed 80 lb. I talked to a frame builder about a custom frame, but he absolutely refused to consider a frame with a custom fork with more trail.
Item 4 is nearly impossible with one battery, I have a 17.5 ah 48v and should have bought a 21 after experience. 2 batteries is a theft hazard, & no, the spare won't fit in my pocket while I'm at the concert. Concerts have metal detectors, no 7 lb batteries allowed. My battery is a PIT* to take off, by design.
1 & 3 were satisfied by the unpowered yubabikes bodaboda, but their electric model had a boat anchor like Bosch mid drive (unpowered) so I bought their pedal pusher model with 24 speeds, after they bragged it could handle 2 children on San Francisco hills. Turns out it is progress on item 2, I haven't fallen off on my chin yet. Maybe because more of my weight is on the front axle.
5 has proven totally doable with a $221 geared hub motor and a $720 battery on the bodaboda.
4 hasn't been tried yet because my hips hurt too badly after 5 hours. A new seyelle seat may make the 100 mile RT concert trip worth trying this year.
I was looking for a non-cargo bike for a lady today, the biggest battery anybody was selling in a small frame I found was 19 AH 48 v. Build it yourself , you can buy as much as you want. No custom connectors to gouge you financially when the battery wears out, or to lose contact when you hit a bump. Just reliable .250 insulated dorman flag terminals.
One special feature no vendor can sell, my hub motor is on the front, which balances the cargo on the back. If some dingbat rode that onto ice, or wet moss, the bike would go down and somebody could be sued. But since I did it myself, I just have to be careful- which I was going to do anyway.
One bad experience, there are only 2 USA battery vendors I trust besides OEM's. Luna & ebikeling. Have amazon & ebay piles of trash waiting disposal in the garage.
False starts, I tried to put a 18 lb battery on the front fork of a Huffy Savannah cruiser, and didn't like the way it swung around. 18 lb batteries were trash anyway. OTOH the bodaboda has fixed mounts up there for a grocery basket, total solution for the luna battery. Been riding it 2 1/2 years, 4000 miles electric.
Next upgrade? Torque sensing control. I hated PAS, too fast & jerky, didn't move the pickup or PAS controller to the bodaboda. Probably before that, electric shift. thumb shifters destroyed my right thumb joint, and twist shifters didn't help either, required pinching the shaft too hard with the thumb. The new SRAM MTB electric shift is only for their 12 speed rear cluster, and everybody knows 12 speed chains last about 1000 miles max. My 8 speed chain is lasting 5000 miles first iteration. Besides there is a patented $69 battery involved. Prototype electric shifter is on the coffee table in checkout. Uses main bike battery.