..just to insert correct information from someone who lives in Indy and has worked for both UA & US....
1) The MTC center in IND is already 75% outfitted. The equipment and tools were for some silly reason bought by the BAA who runs the airport and belong to them. So when UA, left - they actually did an inventory and most of the tools and equipment are there.
2) The Mayor and City-County Council have all been in the paper and on TV since UA left stating that they would seek a tenant, but they would not give the type of tax breaks to someone new that they had given to UA, especially US (there were a lot of rumors in the press on that issue). US would have to have another reason for moving here - but doubtful they would anyway. They had an opportunity in the planning of the new airport that is being built to give their input and were even offered tax breaks to leave PIT for IND as a hub - they said no thanks and instead asked for lower lease rates and lower landing fees. Trying to bite the hand that feeds you may be their way of doing business, but it doesn't tend to work in one's favor.
3) The O&D traffic is not lower than PIT, on US it most definitely has dropped. But that is due to the increased flights by ATA and WN. AA, UA, and DL have all added flights again - the second time in 6 months, while US has cut back.
...on a personal note, as a former US employee - I wouldn't want the airline here. I live here and pay taxes and would ultimately end up paying for the inevitable screw ups that would occur.