Stumbled over this while reviewing #10858. Seem that we have an overcomplicated implementation here.
I think there should be no such things like "statusbar" or "gui" in a non-GUI class (when possible).
Next step would be to handle multi-warnings on RPC level (move from single string to an array).
I don't see any updates to safemode.cpp here at all so I think you lost it in the simplification: GetWarnings contains hidden logic as to what warnings should trigger safe mode and which should not. Warnings only returned with statusbar and gui but should not trigger safe mode (such as the pre-version warning) should not be returned with rpc.
Oh... I missed the new safemode.cpp/h in my IDE search-project!
Closing for now,... maybe I reopen once the safe mode is gone.
Yes I think it makes sense to do this as a post-safemode-removal optimization. We should make sure to deprecate it in the 0.16 release notes.