An antibody based vaccine for flu is gonna be inherently short lived due to the mutation rate in haemagglutinin and neuraminidase, I understand you're saying there's potential for T cell activation with this new vaccine, this would be great (i.e. as it would allow the 'currently' less mutative interior based proteins to be the target of attack), however, given influenza is an RNA virus it has a naturally high mutation rate.
Sure the new peptides presentable to T cells will work as the basis of immunity to begin with, but in making a vaccine targeting these you simply apply selective pressure to these epitopes which will - i suspect - come to be as polymorphic as haemagglutinin and neuraminidase are currently.