Sadly I have to use RekordBox now that I want to not bring the laptop + DJ controller, but just a USB stick. And RekordBox does not run well on Linux (tried VirtualBox and Wine, both failed attempts).
Sadly there's no RecordBox clone, or "export to RekordBox USB" feature on Mixxx.
RekordBox doesn't even run well on Windows, so hard to imagine what worse looks like.
But yeah, if Mixxx (or other FOSS software) could offer writing playlists into USB sticks, I'd get rid of RekordBox yesterday because few software out there works as bad as RekordBox.
Unfortunately it's far down my priority list given the cost, my unfamiliarity with Mixxx development and that I rarely do anything without Mixx.
But this is absolutely what ecosystem grants/bounties should be for.