Something like this or similar.

https://www.digikey.com/en/products/detail/keystone-electronics/5001/255327

Find the right pins to use and add a few buttons.

Choose a board shape once all of the features are locked and implemented.

Add a header for the MIDI UART lines.

Remove the large single row headers remnant from the Sam Littlewood design.

Use a smaller header to bring out all spare mprj lines not used otherwise.

Good candidates:
usb_sof
power rails

Remove the solder bridges and add a 2 pin header for measuring the current of each rail.

Use standard 2.54" header and add shunt to BOM.

Use solder bridge or zero ohm population option to allow an optional 2 pin header for applying an external clock.

Switch the on-board oscillator to something best fits the design.

USB is the main feature so I would imagine 12MHz would be good.

Just what the title says

We only have 4bit video so we can probably use that variant.

https://1bitsquared.com/products/pmod-digital-video-interface
https://github.com/icebreaker-fpga/icebreaker-pmod/blob/master/dvi-4bit/v1.1b/dvi-4bit-sch.pdf

Make sure that it has a courtyard and otherwise aligns with the KiCAD standard silk screen etc.

Add USB connector.

USB-C connectors seems to be all the rage these days so lets go with it.

Header will contain the caravel management pins currently broken out to J1 which is 1.27mm SMT.

The footprint of the ASIC needs to be changed. It is mirrored according to Tim Edwards.

Add a general purpose RGB LED. Can be added to any unallocated mprj pins.

Add a simple RC filter and op amp follower to the PCM outputs.

Bring the conditioned output to a stereo headphone jack.

The KiCAD library didn't have the PCB footprint with the appropriate pin out for PMOD.

Review the connections vs the DVI PMOD and update as necessary.

Even if it is just the pin numbering convention still update it so that it matches the PMOD.

Don't want to zap our precious chips.