Really popular outcome (2,6)
I believe the answer is:
in effect
'really' is the definition.
(I've seen this before)
'popular outcome' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'outcome' becomes 'effect' (synonyms).
'in'+'effect'='IN EFFECT'
(Other definitions for in effect that I've seen before include "In reality" , "to all intents and purposes" , "Really; operative" , "In force or in practice" , "Operating; to all intents" .)