If with a Feather/Wing combo you don't need to worry about 5v/3v, if there wasn't an enforced shape that would not change in the slightest.

> All Feathers and Featherwings use 3.3V logic - so do not make anything that requires 5.0V logic. You must accept and emit 3.3V logic on any Feather/Wing (except for Analog inputs)

Like, the literal shape of the PCB has nothing to do with their compatibility, rules like do.

Same with SPI pins, RX/TX, etc:

> Bus Pins

> To make it easy to create add-ons, we have fixed inter-chip bus pins:

-

The main change vs female headers is now you're forcing beginners to choose something that locks up their hardware.

This isn't a new thing, beginners since Arduino days have been overwhelmed by how shields take over all their pins and often run into clashes.

It's less of a burden if anything to have proper connectors or simply well marked female headers, which newbies can then easily follow between boards.

I mean if even if you're experienced with electronics just try following which pins a board is actually using. You'll need to look up a PCB schematic.

That's infinitely less beginner friendly than simple color coding and fixed connectors.