I don't think the angle of competition with the airlines is a facade. Yes, there are calls at Newcastle and Edinburgh Waverley, but those choosing to fly between the South East and tha aforementioned cities are mostly heading to, from or via central Newcastle or Edinburgh, surely.
It is a fact (I assume, as it's stated in the press release!) that two thirds of the London-Edinburgh market goes by plane. That's a big market to go at, and if the journey times are about 3.5 hours city centre to city centre, then it starts to look attractive. Also, provided the pricing structure matches that of the airlines - which InterCity rail operators generally do these days with expensive peak fares for the business market and cheap AP at other times to fill up capacity - then First could compete with them quite effectively.
As for Stevenage and Morpeth, there may be something in that too given their proximity to their nearest airports. They will need dedicated bus links if this side of it is to work, which connect with (and wait for) the new operator's trains.
There is also some potential to capture passengers flying in medium- or long-haul and connecting out of / into internal flights to / from the north. FGW has recently installed a successful partnership with Singapore airlines for onward travel from Heathrow to the west of England, so I'm thinking along these lines, where the airline issues a rail ticket for onward transfer (although I don't know enough of the airline market to speculate which airlines might be useful for the east coast operation to do business with).
Finally, many a sceptic might (with some justification) assume it's all about ORCATS-raiding the London to Newcastle and Edinburgh pots. What if the new operator chose not to claim ORCATS revenue and focused solely on dedicated ticketing, just like the airlines do? This would concentrate efforts on plundering the airline market. Radical, yes - but could it happen? There must be £millions to be had by doing just that, and it would weaken any legal challenge by Stagecoach/Virgin (which we can probably take as a given that they will do!)
So maybe it's not just sour grapes - maybe it's a new and innovative business idea which really could work. If they are as genuine in their motives as their PR department claim they are, I for one applaud First for having a go and trying to do something different.