avandalen said:
To estimate the size of the market, who has any idea how many bare hub motors are sold worldwide?
Bare motors? As in DIY kits? Keep in mind that based on the posts I see around here and on other similar forums, most of those are sold to people with very low budgets, generally converting a bike that is not even suitable for their usage--so at a guess, "most" consumers of bare hubmotors are not even potentially in your market.
For an actual number, I couldn't even hazard a guess--you'd probably have to check with manufacturers of the motors to see how many they sell as bare motors to places that sell them for DIYers, etc., rather than to companies that build bikes.
If you want a bigger market, you'd probably have to sell to those companies instead (but they will probably not buy it, but instead take one to the place that builds their frames and say "hey, can you copy this real cheap for us?").
What kind of torque limit are you placing on the motors to be used in the dropouts? Looks like it might be fairly low, as even at 10mm thickness, they still look like standard dropouts, which can't really take anything significant (since they're not intended to).
https://www.avdweb.nl/Mavik%20thumbnails/Article_files/Solarbike/Images-mechanical-issues/Carbon-fork/Slotted-U-shaped-dropout-for-hub-motor-fill-442x210.jpg
If you really intend this fork to be used for hubmotors, you could design the dropouts around that purpose, not just making them thick, but with a pinchbolt at the opening, to prevent rotation of the axle, so that the system doesnt' require the end-user to incorrectly mount a random poorly designed torque arm that either came with their motor or that they randomly found on the intarwebz for cheap, and then destroy the dropouts on their very expensive fork.
There are plenty of design examples of clamping or pinching dropouts in the Torque Arm Picture Thread, among other places here on ES, if you need inspiration.
I would also not shape them the way you have there, like "typical" dropouts--I would make them more or less rectangular so the material is still there between the arm inside the fork and the maximum-width portion of the dropout area, which will aid in resisting spread of the dropouts. It adds a little more mass, but it should be stronger this way. You'd have to do stress modelling to see if it is worth doing for your application.