Having the Playdate appear as an audio device via USB would be ideal!
I made more roundabout solution for @ncarson9, which I recently put up on Github GitHub - GamesRightMeow/micaudioplayback: A simple audio playback app for quickly testing audio on a Playdate
Basically you use a TRRS aux cable + mic/headphone splitter (or a virtual cable) to connect your audio out from your computer to your mic jack on your Playdate.
The SDK doesn't support realtime playback, so you do still have to record the audio before you can play it, but its a lot faster than rebuilding and pushing to a device!