I think for optional I'd just write "It may be worth ..." and I think I might prefer using 'Maybe:' as a tag because 'Optional:' implies to me "I'm sure this is a good idea but it's not strictly required" which is enough different to seem worth separating the two.
The FYI tag is a fantastic idea and I shall try and remember to use it in future.
Nit: This is a minor thing. Technically you should do it, but it won’t hugely impact things.
Optional: I think this may be a good idea, but it’s not strictly required.
FYI: I don’t expect you to do this in this PR, but you may find this interesting to think about for the future.
None of these block a merge and anything beyond these type of comments will be a in-person discussion.