Great idea, as the industry/Hobby as a whole, could use one (or more), but to cover all makes, it will have to be very comprehensive and probably quite large.
Then there is the problem of updates and amendments as "better" designs are made and sold...
Furthermore, there is also the problem of the "knowledge and ability" level of the bike's owner, as some of the repair work needed to be done, needs a great deal of background knowledge and specialist tools......and a workshop, in inclement weather, is also needed.
But even some individual manufacturers are (apparently!) loath to put out a decent manual of any sort on their own products, and sadly some expensive makers will not even supply ANY spare parts to private persons/owners/LBS that are not affiliated/trained..... for the best example of that, just look at the way "Bosch" products are 1) expensive, 2)designed to actually "hinder" repairs not made by Bosch, and 3)charge huge sums, 4) sometimes take months to react, for parts (replacement motors are apparently close to 1000 UK pounds, once installed) that may exceed the new price of some simpler (and often far more reliable!) 100% new cheaper e-bikes....
You only have to search through the pages of Pedelec to see that in all its glory!
But Bosch are not alone, but probably the best (worst?) example.....
Basically, that is why (IMHO) such forums as Pedelec have appeared, to supply the needs of a private person wanting to repair and maintain his bike.
Furthermore, a prospective e-bike owner, before paying out any money buying an e-bike, can search on such bike forums and note which e-bikes are easy to repair and obtain parts, and which are not, as it is hopeless relying on the actual manufacturers for such details needed.
I wish you well in your endeavors.
Regards
Andy
