First, I commend you for putting your ideas in front of an audience as well-informed (and with as many strong opinions) as this one. If I may make a suggestion, as you move forward I think you should be very clear not only who the intended users will be, but where appropriate locations for these markers will be. I can think of places where I *would not* want your signs--if I was on your review panel, I'd be asking questions about this. Would your signage really be a good fit for the big wilderness areas in the American West, for example?
You might want to read this article by Ryan Jordan (I think it can be accessed by non-members): http://www.backpackinglight.com/cgi-bin/backpackinglight/mapless.html
It can be argued that humans have always tried to "tame the wilderness with technology," but as I'm sure you know, for at least the past 100 years, people have also tried to preserve some wild places *as* wild places. Your project *is* taking a position with regard to technology and wilderness, and seeing QR codes (or any signs) affects people whether they want it to or not--in my view, you'll need to address that.
Personally, as more and more people move to cities and abandon rural and semi-wild areas, I'm in favor of those places become more wild (ie, less safe). For example, I'd like to see grizzlies re-introduced to much of their historical territory, even if that makes it more hazardous for me to hike there.
I don't mind fencing off wilderness if that's what it takes to keep ATVs and snowmobiles out; but within wilderness I don't want any fences, guardrail, handrails, cell towers, etc. I'm in favor of a lot of road removal, and some trail removal as well. When I see a trail sign that's fallen down and illegible, I really don't consider that a problem.
I understand the argument that hikers endanger SAR personnel if they need rescue (and actually, I'm pretty risk-averse in my own hiking choices), but SAR do choose to take on that responsibility. It strikes me that the people one usually hears about getting in trouble are unprepared overnighters or dayhikers, who think they are on safe, well-marked trails--not sure your markers would change that.
I get that the primary purpose of your idea isn't safety, but opening new possibilities for trip documentation. But because your markers would be a physical presence on the landscape, there's plenty of places where they would detract from the experience I want in the backcountry, whether I choose to use them or not. By contrast, if I don't carry a GPS unit, I can ignore GPS signals as if they didn't exist.