This is something I've managed perfectly safely many a time whilst standing up on a 377 racing across what feels like the face of the moon. Drink in the left hand, rucksack between feet, breakfast in the right hand and lean on a nearby pillar or wall - easy really!
When finished with breakfast, the right hand is free to hold the smartphone or Kindle - who bothers with paper anymore? Far too cumbersome for the modern commuter...
Cup holders would be a nice addition, yes, but ultimately it's capacity that matters on anything that's used on a commuter or airport service - of which Thameslink is both. I will miss the tables, but I'll live...there is always the option of just using a 377 or 387 operated service in the south or an EMT service in the north - and are the journey times on GN services where there isn't a VTEC option for at least some of the distance really that lengthy, given there will be a variety of the older trains available on that route, too...
For now I'm happy that we're getting brand new trains, which will be much easier to circulate in when quiet, and have massive capacity which is desperately needed when busy...I'll reserve any further judgement until I see one for real and get to travel on one - I'm sure there will be some moditifacitons in their lifetime.
For the majority of GN users, the class 700 will be the only option - especially off-peak.
Personally I'd have preferred a service along the lines of
1tph Kings Lynn - KX fast from Cambridge (377)
1tph Cambridge - Thameslink (semi-fast) (700)
1tph Cambridge - Thameslink (slow) (700)
1tph Kings Lynn - Thameslink fast from Cambridge (700)
1tph Cambridge - KX (semi-fast) (365 or 377)
1tph Letchworth - KX (slow) (365)
1tph Peterborough - KX (365)
1tph Peterborough - Thameslink (700)
The reduction in services through the Thameslink core would reduce some of the issues surrounding loading times, in turn allowing a more comfortable interior, in turn allowing Cambridge to benefit from faster journey times into Thameslink, and also allowing Kings Lynn to get more capacity and through journeys.
I'd also look at making all 700s 12-car. Locking the Cambridge-Tattenham Corner service to 8-cars is not helpful, if capacity really is so vitally important the 8-car 700s wouldn't have been ordered as such.