Wiki Article of the Change
https://en.wikipedia.org/wiki/Unicode_in_Microsoft_Windows#cite_note-10
One of out customer had selected that and we started to experience very weird problems and took some time to find out why it misbehaves.
None of the application could connect to Firebird SQL server (Ours or third party) successfully.
So would be smart to go through all tooling and code with that setting, we never know what M$oft will do with that, will it ever be released or will it soon be default for all.
One coder switched this on and started to get weird results, he could not specify what all symptoms, but said that lot of work to be done before that setting can be enabled.
Could be smart to Check how your environment, tools and code will behave.