This would be such an enticing project to jump into, there are just enough bits to make it seem doable, even if the realist in me knows its not really feasible.
Intrigued by that, I went looking. First commit of support was 2019, for Linux5.2. Yet, 5 years later, there is not one example (that i could find) of OpenWrt running on these Chips. If the platform/FW/BSP package were any good, I'd expect there to be chat about it in the forums, and/or attempts to port to such devices from SMBStaX (The Microchip BSP Linux dist).
I suspect it's not worth the effort for most people. People who want to DIY a switch are likely content to brute force it with a decent cpu, multiport network cards, and lots of PCIe lanes. While others will be happy with a used enterprise OEM unit.
Does make me wonder what asics Microtik is using under the hood though...