As an outsider, I think Pacioretty for RNH with a minor addition from Edmonton is a pretty fair trade.
RNH is overpaid at $6M and has 4 years remaining (including 2017-18) on his contract, has not lived up to expectations and is known to play somewhat soft. But he's also only 24 years old, a Centre and has good vision and a nice set of hands. He could thrive without the expectation of being the #1 and a couple of big wingers who can skate.
Pacioretty has an affordable contract at $4.5M for the next 2 years (including this) and has been a consistent scorer who hasn't scored less than 30 goals in a full season since his 2nd year in the league. On McDavid or Draisaitl's wing he could be deadly. But he is 28 years old and a UFA in 2 years.
Reasons this works - Habs lack play makers at C and some of their core (Plekanec, Weber, Price) are aging out quickly. RNH, will never put up the numbers Patches has, but without a better transitional game (puck moving D and play making C) Patches may not put up those numbers again. RNH could also allow MTL to move Drouin back to the Wing, where he is probably better suited and balance out their attack. But they still need a better puck mover on D than Weber/Alzner/Petry or what ever they have back there. For Edmonton, it's all about NOW. With the Drake Caggiula and Kailer Yamamoto developing well, they can probably do without RNH and would achieve greater balance and scoring depth by moving Draisaitl to C on the 2nd line. Additionally, Edmonton HAS to move contracts by the summer to make room for McDavid's massive extension.
Reasons not to do it. For MTL, Nugent-Hopkins is another tweener. Do you give up a perennial 30 goal scorer on an affordable contract for a C who has not carried a line and has never put up more than 56 points / 24 goals - at $6M per for 4 years? For EDM - patience young jedi - Puljujarvi is only 19 years old and could be as good or better than Pacioretty for much longer. Also - Patches hasn't exactly set the world on fire so far this season, but 8 games isn't really a trend.