Latest update, the power module is almost fully complete. To help anyone else attempting a similar project, I figured I'd outline what I've done, and how everything works, now that I know it works.

The requirements for the DSpi power stage are fairly non demanding. I am going off the Raspberry pi 5 power specifications, as it uses most of the same hardware as the compute module 5, and is freely available. The RP5 requires 5 amps at 5 volts for full operation, which is a stupid specification for numerous reasons, most notably that almost all USB power supplies, even fancy USB PD ones, only provide up to 3A of current. Luckily, you can run a RP5 off 3 amps, with a restricted USB power output (down to 600mah). 

Since we need the thing to be portable, we need a battery, and PMIC solution, as I have discussed in the previous entry. In this case I am using a single 5000mah Lipo, with a BQ25890 BMIC chip from TI, and a TPS61022 boost converter to supply the system, since we need to push the lower battery voltage back up to 5v. A STM32 MCU is also included on board, as the BMIC has some I2C registers that must be set on start-up, such as peak charge current, input current limit ect. Components are connected as per the diagram below:

Of course, each IC needs its own auxiliary components, especially for the buck converter and BMIC modules, meaning the full design is quite a bit more complicated. Luckily the reference layouts provided by TI work decently well, and are easy enough to understand. 

After a bit more design work, I now have a fully functioning board, and the pi now works both off, and on charge. I'll probably publish proper design files on github later, but for now, here is the design schematic, as reference for anyone interested.

Now that the power work is complete, we can get into the fun stuff, and get this device looking more like an actual console. Some super secret stuff I've been working on is below.