Linux 5.15 has been released and while going through changes it seems MIPS support is almost done, there were very few patches and even in past few year main contributor has been Loongson and now they have dumped mips for their own new architecture called loongarch. This is an indicator that when deciding on new SOCs once should pay attention to SOC CPU architecture and if its not ARM, RISCV or x86 then take a double look
Nice Details of changes are here Linux 5.15 LTS release - Main Changes, Arm, RISC-V and MIPS architectures - CNX Software