Assuming Machester-Luton would primarily be a business route. It would not work, simply that the time taken to get to Manchester airport, check in, fly to Luton, get a taxi to Parkway, get a train to London, would take too long compared to Mr Virgin Branson and his west coast train line?
BMI make it work from Heathrow, so what do I know, but I do know that Luton-Liverpool by easyJet was doing well with passengers numbers, but yeilds and profit were higher using the aircraft to go to Spain, so easyJet pulled it!