OK, I've been to Iceland at the end of June specifically for shooting so a few thoughts.
Firstly, can you really buy a Sony with those lenses for the price of selling your Nikon gear and a couple of Nikon lenses?
Given that this is only a trip, will you miss your nikon system when you get home? Changing system for a trip only seems to be counter productive to me. A system is decided on for years of use not just a one off.
Are you up to taking a new system on a once in a lifetime trip? Are you ready to switch RAW converters given that ACR/LR seem to be bad for Sony files? Will you have sufficient backup? If everyone there is shooting Nikon/Canon then the ability to borrow someones long lens or macro lens or whatever cannot be underestimated. To be honest I wouldn't do this without full backup anyway of camera, lenses and even stuff like cable releases.
The light changes stupidly slowly in Iceland in the summer. I also didn't meet any serious wind. If you're shooting landscape then just stitch! Takes under a minute to stitch about 40 megapixels in the 2:3 format and I do it with just a ballhead panning head and a RRS PCL-1. I've never needed the whole nodal point stuff either and Autopano Pro ($99 for the latest version) has zero issues with moving foliage, waves, etc between frames. Also never has any parallex problems. As such unless you are willing to commit to the Sony system (including after you get home) I'd say that stitching is going to be the answer to your need for more megapixels. An added bonus is that when stitching your wide lenses become much wider, you won't need that 14-24 but you might well need that 200-400VR lens or an equivelent. To be honest with the amount of resolution gained by stitching, heck, a 1.7X teleconverter on a 70-200VR should be plenty sufficient.
I've no problems with the Sony system but the idea of switching systems just to use it on a workshop, taking a system that very few will be sharing on that workshop, having to provide for expensive backups and the fact that Iceland in the summer and landscape photography is a stitching photographers dream - I would think very carefully...
BTW, take a mosquito net. Myvtyn has so many it's almost impossible to breath eventhough they don't bite.
Taken with a lowly 1Ds, oh the horror of only 11.1 megapixels!