Both sides are opinionated, but the mirrorless folks seem far more cheerful, which is understandable because our favored technology is ascending, not disappointing before our eyes. Maybe happy people are more prone to look at new technology, who knows? I was hoping to learn why live view of nature is so important besides battery life, and asked politely. Do you know?
I don't do serious nature photography but my understanding is the issues with an EVF for nature photography are:
eye strain - which seems to be an inherent issue with screens, at least with existing technology - because people may be spending very long amounts of time continuously with their eye to the viewfinder as they watch and wait for the opportunity to get the shot they want
lag - the opportunity to get a shot may be fleeting, and unlike many sports where you at least have some opportunity to anticipate what is going to happen and could take a burst covering the relevant moment if you didn't want to rely on timing your shot, you may not have much if any warning of when the interesting moment is likely to happen so taking bursts may not be the answer
battery life - spending very long amounts of time continuously with your eye to the viewfinder means you are chewing up batteries if the viewfinder is an EVF. As battery technology improves and the components of a camera (including any EVF) become more power efficient, battery life may (or may not) cease to be a practical issue, ie even if a DSLR would go for longer on a single battery, a mirrorless camera may last long enough - we will see.
exposure preview in the EVF may not be something a nature photographer wants to use, because they may want to keep their eyes adjusted to the ambient light rather than look at relatively bright image in a viewfinder and then have to readjust when they take their eye away from the viewfinder. I assume you can make an EVF dim so that isn't a problem if you want, but what I'm saying is that one perceived advantage of a EVF may be lost at least to some degree on nature photographers.
I'll be interested to see if those doing serious nature photography correct and/or add to that list.
On another note, from what I read around the internet, my feeling is that it's the mirrorless folk who often seem more determined to say that mirrorless is a fundamental change and mirrorless is so much better than DSLRs that DSLRs will be swept away, while the DSLR folks are more likely to be happy for others to use and enjoy mirrorless cameras while simply pointing out that DSLRs still offer some things (at least at this point in time) which some people consider advantages so DSLRs shouldn't be written off.
As I've said many times before, for my own part I ultimately do not care whether there is a mirror in my camera or not. I do care about how much I enjoy using my camera for photography - and how much I enjoy it reflects in part the results I get and in part what the process of taking photos is like. At least with current EVF tech, I simply enjoy the process of taking photos less with an EVF than an OVF. Whether that will change at some point as EVF tech develops, or whether mirrorless will ultimately offer advantages which mean I decide to put up with an EVF to get those advantages, we will see. I am pretty happy with my existing DSLR gear though, so I'm not betting I will buy a mirrorless camera anytime soon (and perhaps I never will?). But as has been said by others above, there is no reason to think DSLR tech will stand still either, so we will have to see how DSLRs develop as well as how mirrorless cameras develop. (I, for one, am looking forward to independent reviews of how the 1DX III's AF performs for accuracy with wide apertures compared with mirrorless cameras.)