I simply cannot see the demand for 4tph from Bedford to Cambridge existing unless a big load of new eco-towns with new stations were to be developed along the line of route (think a big load of Buckshaw Villages, perhaps five or so of them along the route), and even then 2tph of longer trains would likely suffice.
A big load of new eco-towns are going to be developed.
When I moved to work in Cambridge in 2000, on a scientist salary, I could have a nice house in a nasty part of Cambridge, or a nasty house in a nice part. In Ely, I could afford a nice house in a nice part. Now you would need two incomes to afford that, or to move further out.
With two incomes, you then need to live somewhere within commuting distance for two jobs.
Science jobs can be pretty specialised, so you don't have a lot of choice. The last time I had to look for a job, I had choices in Cambridge, Ongar which would have been a 60 mile drive, or Oxford, which would have been a move.