Up to now, one has a right to a seat (2,3)
I believe the answer is:
so far
'up to now' is the definition.
(I've seen this before)
'right to a seat' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to a' says to put letters next to each other (I've seen this in other clues).
'seat' becomes 'sofa' (sofa is a kind of seat).
'r' after 'sofa' is 'SO FAR'.
'one has a' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for so far that I've seen before include "To this point" , "Up until the present moment" , "till now" , "to a certain degree" .)