It is definitely a must to try and find downsides and weigh them, but even with RISC-V thrown into the mix, the situation will be far from what it was 25 - 35 y

It is definitely a must to try and find downsides and weigh them, but even with RISC-V thrown into the mix, the situation will be far from what it was 25 - 35 years ago, and in addition the tools are much more advanced. Modern compilers can already deal with several permutations of ISA extensions. Of course, there are limits to everything, so having everyone and his grandma creating his own extension will be messy / ugly...