My comments over the spare 31x 319 only applies to 2015. By the end of 2016 all 86x 319 will be spare so there is something like 72 units to be allocated future duties.
Currently looking like Thameslink will release something like this;
2014
3x 319
2015
32x 319 (29 from 387 + 3 used for C4 cover from 377/2 cascade)
2016
41x 319 (from 700 introduction)
10x 387
2017
25x 377 (for Southeastern)
2018
19x 387
377/2 & /2 fleets will be cascaded internally within TSGN for Milton Keynes services.
Well by your reasoning why did the 317/7s and 319/2s need a special Airport interior, why wouldn't the standard one without tables and with 3+2 seating have sufficed? Have the 319/3s even been used on Airport services or are you just saying that because 319s have been used on Airport services?
The point I was making about the interiors was that they will be inferior to the current interiors and the interiors on the other fast Manchester-Liverpool services. If you want passengers to use the new 4 car service opposed to actively try to avoid them then you need an interior as good as on the 185s and the EMT 158s.
The 319/2 interior has nothing to do with the Airports, in fact quite the opposite. They were built to serve the Brighton Express that doesn't stop at the Gatwick (one of the few trains that doesn't). The idea was rather than a trolley service like now, they had a bar there serving food with a lounge area. What's happened since is the special areas have been removed to provide more seating.
All types of 319s have served both Airports with the 319/4 refurbishment actually including more luggage space as they are aimed more to serve the Airports and carry far more passengers with luggage (which includes Eurostar travellers too) for many years.
Of course the 317 were for the Airport premium service (including price) with local stops for links just like the 379 today and even 442 which justified a different interior. Northern doesn't currently have a premium service does it? (Last time I came home from the Airport it was on a stopper pacer via Warrington Central).
The question I now pose is will the passengers (mainly off peak as they get the bigger capacity increase) who have just flown home really care too much about the modern interior compared to other trains when they are more likely to get a seat?
As for being n the same level as the 185, that is upping the cost of renting the units according to many in the industry so where does this extra money come from? Better units but higher ticket prices? I think comparing a 319 to a 185 is missing the point. You have to compare the stock it will replace and also look at the market. Getting home and getting a seat are very important factors for choosing a train over driving for airport travellers who are more suited to get a train home than drive the whole way back.