I'd take the mirrorless travelling, and have the SLR for more specialised shots.
But depends how you travel, if you're taking a 600mm f/4 IS II, the camera on the end won't make much difference if it's NEX-sized or a 1DX.
What specialized shots would those be? Just curious. I take my SLR when traveling because (a) I want the full functionality it offers; and (b) it really ain't that big. With a couple of primes - say 85mm and something wider - it fits easily in my briefcase.
I'm not sure really, tbh. For now, at least, dslrs offer much faster and better phase-detect AF, so the 7D stays for sports.
In really low light, I trust my own eyes (and my katzeye) better than waiting for live-view to update, the back screen can be a bit jelly sometimes (which I hear is a real problem with Sonys, of course having never used one myself).
And I've just been taking pics of the 'supermoon' tonight, maybe it's a problem with the 7D, but taking a wide-angle shot and trying to MF on 10x live-view is impossible, the screen amped up the gain because most of the scene was black, it blew-out the moon, impossible to focus on a bright white blob. So I had to use my katz-eye viewfinder again for that. (but then after a while I though about focussing on a dimmer star instead).
For most other purposes IFF the lenses were of the same quality (hopefully smaller size), iff the battery lasted just as long, iff I could get all the other things I like about dslrs (accessories, TC80, RC6, speedlites, flash-sync plug, +/- EV bracketing, (at least) 3 custom modes, IS), iff (and when) the AF gets fast enough to rival a 7D, iff it was in a body size/shape I could carry around all day (frankly, my 7D and 70-300L is a very easy combo to hike with), and iff it did all this for a reasonable price with at least an aps-c or bigger sensor, then i'd certainly love a mirrorless.