I've traveled now for several years and many weeks on the road with an iPad & iPad 2, both with 64GB ram, including three month-long trips to Europe where size and weight were factors.
I have the connection kit and the SD dongle. I shoot with both Nikon D800 and Panasonic GX7 bodies. Until iOS 8 came along, I could edit my raw files with iPhoto. Now I use one of the other apps on the iPad but don't remember which other than it will handle the raw files.
Downloading is always slow no matter what. For the D800, I use a USB-3 cable. For the Panasonic, I use the SD card dongle. The thumbnails from the D800 move along, but selecting is from an image that's perhaps a half square inch of real estate. Down loading from the dongle is extremely SLLLLLOOOOOOOOWWWW! A 32GB card will take at least a half hour or more…just to render the thumbnails. Don't even think of trying a filled 64GB card (I did once and that was enough, especially when I bumped the dongle 45 minutes into rendering…then started from square one taking more than an hour!) There's no rhyme or reason to what is rendered first. It seems random, sometimes from the start, sometimes from the middle, sometimes from the end of the card. You wait a long time to see the images, select them, and in a few minutes, they are downloaded, the fastest part of the operation. The tags stay with the images on the card so you known what's been downloaded previously.
Shooting raw files, you need to find an app that will work with your camera raw files. Usually, the tools are rudimentary but enoung, even when iPhoto was compatible. I was able to process any files to convert to jpeg for email and fulfillment along the way. An iPad can also easily download your video files, though I am not sure which formats are supported other than MP4. All the images are stashed into the Photos app and each download is kept a separate group, even additional downloads from the same card.
I started traveling without my MacBook four years ago so as to save a good six pounds between the MBP, brick and accessories.
Traveling this way is lighter and simpler but takes patience. Because I'm downsizing to the Panasonic cameras for my main travel cameras, I'll probably go with a iPad Mini 128 since it is smaller and lighter and everything fits in a very small bag compared to a large, barely-overhead bin fitting and very heavy (16KG) backpack.
You can function with these tools, but know that even though it is smaller and lighter (great to me!) it all has limitations and creates other issues you need to workout before your trip.
