I would suspect you are correct here, I can easilty see Kettering becoming an extension of Thameslink!
Probably quite true.
Frankly what's wrong with that? Compare some mileages:
London to Bedford: 49.75 miles
London to Kettering: 72 miles
London to Leicester: 99.25 miles
London to Southampton: 79.25 miles
London to Bournemouth: 108 miles
At the moment, London to Kettering is typically just under an hour with HSTs or Meridians. London to Southampton is 74 minutes with class 444 or class 450 (I think) EMUs. Those were quite pleasant to make the London - Southampton trip in and I can't see why a similar distance trip on a newly electrified MML wouldn't use some sort of modern EMU.
I wounldn't mind that trip on either of an updated 350 or 377.
I think the question is:
Where will the new outer limits of suburban EMUs be?
Will it remain Bedford? (I doubt it).
Will it extend to Kettering (and Corby)?
Would Leicester make more sense?
The second question is would Derby, Nottingham and routes northwards maintain an Intercity type service?
Would this then run fast (or at least limited stops) from Leicester to London leaving the intermediate stations to the suburban service?
Lots of unanswerable questions there but I'm fairly sure that if the MML is electrified it'll be running many. many suburban EMU's over most of its length and there will be fewer Intercity style services.
Cheers,
Jason