Old soft page would become paper, in future (4,4)
I believe the answer is:
wood pulp
'paper in future' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'old soft page would become' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'soft' becomes 'p' (musical abbreviation for 'piano').
'page' becomes 'p'.
'become' indicates anagramming the letters.
'o'+'p'+'p'+'would'='oppwould'
'oppwould' anagrammed gives 'WOOD-PULP'.
Can you help me to learn more?
(Another definition for wood pulp that I've seen is " Material from which paper is made".)