Several points here......
1) By making the shuttle fleet type all coach class, you created a sub-fleet type that made changing aircraft difficult and confusing. By standardizing the seat configuration, we improved reliability as there are more options available when there are unexpected ETR's and ATC delays.
2) Having a "First Class" product gave us a marketing tool to seal very lucrative contracts by offering F seating for a Y price.
3) It takes 13-14 airplanes to operate the Shuttle markets.
4) Seat width difference between the A319 and the E170 is one inch, definitly not something that someone is going to truely recognize.
5) Looking at todays Shuttle flying, if we were to use the E170 to fly all of the 94 weekday Shuttle flghts, 54 of them would have been oversold (and that does not take into account the walk up ticket sales). Some of those oversales would be in excess of 40 customers. So do we give up market share to operate the Shuttle with a smaller airplane?
Yes there are certain off peak times of the day that the E170 would be the perfect airplane to fly the Shuttle route. But to replace mainline flying in the lucrative shuttle market with the E170 would not be a wise move.
LightYears......are you sure you are not a salesperson for Embraer? Your obsession with this airplane is on the verge or unhealthy!