@drlobo We do handle some special GPIO buttons. Still not yet shipped in Recalbox itself, but we know it's working and we should include it in a coming release.
But they can't be combined with the GPIO arcade buttons of course, unless you wire your sticks and buttons in I2C with a MCP23S17, thus freeing most of GPIO for this matter.
Still, I don't know if OP wired his inputs on GPIO or on a dedicated USB board. Nevermind, reading the doc would have spared everyone some time regarding the hotkey cheat sheet, that's all I wanted to point out.