Rock band, popularly, coming on board? That’s worth mentioning (8)
I believe the answer is:
quotable
'rock band popularly' is the definition.
I can't tell whether this defines the answer.
'on board? that's worth mentioning' is the wordplay.
'on' is a charade indicator (letters next to each other).
'board?' becomes 'table' (both can mean food).
'that's worth mentioning' becomes 'quo' (I can't justify this - if you can you should believe this answer much more).
'table' after 'quo' is 'QUOTABLE'.
'coming' is the link.
Can you help me to learn more?
(Other definitions for quotable that I've seen before include "worth citing" , "worthy of mention" , "suitable for recall" .)