This is a reach but I wanted to put in two cents about the physical design.
I use a fair number of Feathers and Photons already. I really like them but there is one huge irritant that you are copying.
The battery connector.
I understand the battery connector is standard but it adds a lot of height to the boards. In products it adds a height requirement to the entire product just to accommodate the battery connector.
So, would it maybe be possible, at least, to purchase boards without the LiPo connector soldered on? Or better, a short lipo connector. Or, best, you could actually remove a small square of board and lower the connector.
Thanks for listening.
postscript: I checked an actual product and the current product height is 0.60". Without the LiPo connector the product height is 0.50". Pretty significant difference in packaging.