Nothing wrong with wanting to stick with a DSLR, but if the reason is primarily for your wife's benefit as a PJ, it might not be the best move for you. I once shared a system with my wife too, eventually she got her own (it took some time due to the associated costs of course) and this made life a whole lot easier for us both :) You could argue that a mirrorless would work for her just the same, and would lighten your load for backpacking trips.
Here are a few random thoughts, to confuse you...
- It's hard to come up with any advantages to using a DSLR with kit lenses, over say a high end point and shoot camera. The image quality from those lenses won't make the most of the APS-C sensor in your camera body, and they're not fast enough to produce shallow depth of field for subject isolation (the "slr look").
- Using a single prime is fine, but it's not a shooting style most casual photographers are comfortable with. It takes a lot of practice and discipline and may be frustrating. Pairing a fast prime with a zoom lens however is a good minimal kit.
- 35mm lens is roughly the equivalent field of view as a 50mm lens on a full frame camera. It's not wide, nor does it have much reach. That's called a "normal lens".
- Shooting wildlife in the distance is a niche. This is the kind of stuff 300mm - 800mm lenses are made for. They're big, heavy, expensive. Depending on how far away, 300mm just starts to scratch the surface. Ask yourself how important this is because it's one of the few reasons to still use an SLR (due to availability of telephoto lenses). Unfortunately you have to be fairly committed to carrying a heavy kit once you go down that road.
- DSLRs are still a viable platform, but unless you need advanced AF system, telephoto lenses, or simply cannot work with the ergonomics of any of the mirrorless bodies out there... it's hard to think of a reason to go that route.