There has been some discussion in the past. We still have not really committed to using composer as 'the' way to install cake3 so using any other libraries (like monolog, and php-fig/log) is still undecided as well.
I'm not a huge fan of the bonus classes like LogLevel that it provides, but I think adopting a broader standard would be worth the somewhat over-engineered internals of php-fig/log.
How do you see features like scopes working if we were to use monolog and would Log (the static facade) continue to exist?\
-Mark