And yes, I know it would never happen for so many reasons but would you hang up the phone on either side for something along these lines as a starting point.
Edm: Subban, Plekanec, 1st 2015 or 2016 (whichever, maybe only if it's even needed but likely)
Mtl: 1st 2015 (McDavid), Purcell
Montreal could then acquire the rights to Mike Green or just wait for free agency to get their replacement for Subban.
Edmonton has a ton of young talent up front. Chiarelli had Bergeron in Boston and Plekanec would perform the same task for him in Edmonton as a 2nd line centre to Nugent-Hopkins. Edmonton would also get a solid top 10-15 defenseman in the league to finally give them the guy they so desperately need on the back end.
At the same time, Montreal gets the elite forward player that they are extremely in need of as well in McDavid.
Outside of additional deals or signings:
Top 6 Edmonton
Hall - Nugent-Hopkins - Eberle
Pouliot - Plekanec - Yakupov
Top 6 Montreal
Pacioretty - McDavid - Gallagher
Galchenyuk - Desharnais - Purcell
I think that is a good top 6 for Edmonton giving them someone who can actually teach the youth how to play 2-way hockey and they're backed by a defense core that now includes Subban.
Montreal would still need work but I'd still consider trying to move Desharnais or Eller, preferably Desharnais and going after Matt Beleskey, Justin Williams or another winger to fill the top 6 and allow Galchenyuk to move to centre behind McDavid.
Montreal's defense would hopefully be along the lines of:
Markov - Green
Beaulieu - Petry
Emelin - Gilbert
The money in my opinion would be far more balanced across Montreal's lineup as well.
So basically you are saying give up on the next couple of season. Possibly waste Price in the prime of his career, waste Markov in the final couple of season and hope the team has something to offer in 203 season when McDavid is in his prime?
Way I see if, Habs outplayed Tampa in much of their series who then in turn outplayed NYR and now Chicago. So what if instead of Desharnais, the team had a Staal or a Thornton or a Koivu?
What if instead of Parenteau they had a Stewart or a Stafford?
Habs are not that far off so blowing it up right now even if it means a possible McDavid is IMO not the answer.