No more EMUs are needed for 2 years (end of 2016).
A lot of work has to be done before the long-term Northern fleet is decided.
Until then they have to muddle through with cascades from the 14x319s.
That's assuming Blackpool electrification is behind schedule and stays behind. Liverpool South Parkway - Blackpool North should have gone over to electric in May 2016, with the services via Chorley following in December 2016.
Although, it looks like the MP was avoiding the problem when answering the question:
* Northern apparently have a guarantee they won't lose any DMUs when they get 14 x 319s for extra capacity and don't have any need to take on extra EMUs before the end of the franchise in early 2016.
* Chiltern can take TPE's 170/3s from May 2015.
A couple of extra 350s for TPE on a permanent basis would partially solve the problem but wouldn't stretch far enough to replace the 170s.
EDIT: Actually I wonder if that could be the plan. A couple of extra 319s for Northern to run the Airport-Piccadilly stoppers, to allow 2 x 323s to be sub-leased to LM, to in turn allow 2 x 350/3s to be subleased to TPE.