i think we will see the big carriers come in when the shop refurb is done
I don't believe a refurbished shop will matter one jot in the decision making process of "big carriers" regarding opening services to STN.
Stansted already has two "big carriers" - in EZY and FR - and they serve the niche in the Southeast England market that the airport has made for itself.
Unless and until getting extra slots at LHR, and then LGW becomes too difficult the chances of STN getting "big carriers" - by which I guess we are talking UA, AA, SQ, EK, etc are but two - Bob Hope, and No Hope.