Joined the party late, but based on the hints we've been given, there seems to be three possible outcomes to this situation, which we'll find out at the end of this arc.
1. Timeskip
Let's face it, Luffy's been through tough battles before where his recovery period has taken days at a time, but never has it been like this. He was fatally poisoned by Magellan, brought back from the brink after undergoing a rigorous hormone-inducing recovery (which will only work for 24 hours), helped to spearhead the mass breakout from Impel Down, and joined the battle at Marinford, where he was just nearly killed by Kizaru. Add to this the emotional stress he's been suppressing about wondering where his crew is and whether they're OK, and his desperate need to save Ace, not to mention the shot of vigor hormones Ivankov gave him this weeks chapter and we can safely assume that Luffy will be out of commission for a while after this war is over.
If Oda does decide to go the timeskip route, the time Luffy spends sleeping, which I can see being up to weeks could showcase the rest of the crew and their adventures, on their way back to Sabaody Archipelago. That's the only forseeable outcome I see in this arc. I doubt Oda would go the Naruto/DBZ "training" route for the timeskip, it's not his style (thankfully).
The longest I can see this skip lasting? Anywhere from a few weeks to a year, which could age Luffy up to 18 as well as the rest of the crew too.
2. 27-year-old Luffy
Just like Son Goku before him, we could see Luffy grow to be an adult in the course of this series. This seems to be the most likely outcome, since Ivankov's comment about the hormone recovery process taking 10 years off his life wouldn't really affect the story when it's estimated that the journey around the world is just 2-3 years. The there's the fact that Oda said that movie 10 was LUFFY's last adventure as a 17-year-old and fans should "burn it into their memory". The fact that he wouldn't mention anything else about it, also seemed to suggest that it would affect the story in a big way in the culmination of this arc. Also interesting to note, Luffy would also be the same age Shanks was during the first chapter, don't think that'll really have any special bearing on the story though.
Can this work? Why not? It's Oda, he's been known to take any ridiculous sounding idea and make it plausible, so why not an adult Luffy? He'd just better have a good reason for doing so, which I don't doubt he has.
3. New World is just THAT fucking intense
We've had a lot of fun, adventurous arcs throughout the Grand Line and while they're all well and good, we know nothing of what the New World brings now, nor what it will bring after the Rescue Ace arc is over. It's obvious one must be completely serious about their ambition if they're willing to brave those unknown waters. Maybe this arc's resolution will serve as a coming of age plot point for Luffy, realizing that the time for being a kid is over and if he plans to head for the New World with the rest of his crew, he must be fully prepared mentally. That is I don't think the adventure aspect of the story will go away, I can just see Luffy becoming much more serious about his dream and his crew, after nearly losing both in this arc. And if Oda wants, he can throw a birthday in there too.
Those are my ideas anyway, discuss!