It's not really "less constrained" in any way that matters, though. Sure, you can write more than 8K of Lua and the display resolution is a bit wider, but you don't get a dedicated DSP+sequencer for audio, multiple graphics layers with affine transforms/color math, SRAM(!), a real-time clock, etc. I can't even build a Tamagotchi with this ;)

In other words, for my needs, TIC-80 is still entirely dominated by just using https://github.com/rust-console/gba to write GBA homebrew in Rust. (And everything has a GBA emulator. Everything!)

A viable PICO-16 platform, to me, would have to offer a clear improvement over the "GBA homebrew in Rust" solution.

(Even if all it is, come to think of it, is the GBA's ARM7TDMI ISA extended with some more hardware registers and instructions, and a PICO-8-like IDE for building those "GBA+" ROMs. Such an approach would come with the benefit that you could build a PICO-16 runtime by just starting with a GBA emulator and adding features. You could even choose encodings for the new ops such that they would look like NOPs to old GBA emulators, making PICO-16 "GBA+" ROMs gracefully degrade into regular GBA ROMs when run on a regular GBA emulator—very much like how Gameboy Color games work, or how SNES ROMhacks and homebrew support the MSU-1 audio chip.)