Now that this thread has come back to live, what is the answer for the masses to be able to retain some level of access to horses?
I feel like I spent my youth and young adulthood honing the ability to keep horses, even competitive ones, on a shoestring budget. But what worked 10-20 years ago doesn’t necessarily work today.
I agree self care/co-op style boarding is where the puck is heading… but that has serious geographical limitations. Your horse needs to be located conveniently to your home and/or job.
Something I’ve really been thinking a lot about is DIY farriery. Our glue on technology has improved to the point where the acts of forging, shaping, and nailing metal shoes can be bypassed with adhesive products, changing the learning curve and making it slightly more accessible to the “average Joe.” But this really isn’t ideal for most people.
Virtual lessons could reduce training costs in some instances. Or canned instructional programs (ala RideIQ, Ridely, etc.). It’s not going to work for everyone or every situation, but it’s better than the masses all attempting to go it alone because they can’t afford training.
Along those same lines, I’m seeing more and more virtual challenges and virtual shows pop up, so us lower level riders can get some feedback and feel like we are doing something without the expense of a true competition.
We all could get really into bareback and bridleless riding to reduce our tack costs? 
As for the cost of horses themselves-- there are always going to be free/cheap horses. Always. It’s a non-issue in my mind.
But I don’t know how you can feed more cheaply. I don’t know how you can reduce veterinary costs. I don’t know what you can do about rising land costs. I don’t know what you can do about rising cost of materials.