There are tons of these little "retro console" devices lately—the Bittboy, LDK-game, etc.—that people just treat as emulation devices, when they actually have hidden potential for running native game software as well, with more power than you can get out of them through an emulator. (They're actually usually as powerful as the original PSP, but only have the GPU capabilities of the GBA, making these consoles into a sort of unique alternate-history blend of 2001-2004 era gaming.)
But no games are being written directly for these devices, because they're all slightly-differently specced: different screen-sizes; different amounts of RAM; etc.
A hypothetical PICO-16 "platform", in my mind, would basically be an abstraction over the cross-section of native capabilities of these devices (with maybe some additional tasteful constraints on top), while still allowing to take advantage of the full hardware in a way you can't by just e.g. writing SNES or GBA homebrew.
Maybe the "platform" could even come in a few separate "profiles", where games could be either targeted to a specific minimum profile, or could respec themselves to the highest profile supported (sort of like how Z-Machine games work in detecting the VM's multimedia capabilities.) Take it far enough and PICO-8 could just be the base PICO-16 profile!