@ppoirier - thanks for the link 
I have a tendency to go down rabbit holes - the flight controller “brain” transplant looks like a fun rabbit hole but it’s probably too much for my current project, so your link is exactly what I should be looking at.
@stephendade - I was just about to ask if you’d looked at adding encoders, but you beat me to it In your blog post, you say one needs “4 spare AUX ports” for this. Why four? In the Romi user guide in the section on quadrature encoders they need just 4 pins (only 2 of which need to be interrupt capable) for the two encoders.
Is it that you can only use the RX line on each UART for input? Is it impossible to use the TX lines as GPIO input lines? If I’m reading the F4 datasheet correctly (which I’m probably not) then all the UART pins can be used as plain GPIO pins.
I see that the Kakute F7 has more UARTs. Is this enough? If so I’m happy to sponsor purchasing one for your development - I’d be very interested in seeing work done in this form factor rather than a Pixhawk.