A few of things here:
-I'm not sure if there is really room for those back supports. Wouldn't your knees be cramped as hell against the back supports in front of you unless they were straight up and down?
-They wouldn't create any new revenue(unless prices went up) like the expansion does, so it's just less likely to happen.
-The temporary chairbacks only look bad in a completely empty stadium like the pic you posted. They are totally not noticeable in a stadium even 75% full.
As someone who had battled back problems, it would definitely be an improvement, but I doubt it will happen anytime soon.
using the above picture to base my opinion on, i think there would be plenty of room. look at the widest portion...thats not exceptionally wide compared to the other concrete steps...it just looks like it narrows based on perspective. so, assuming that this is the standard width, look at the 2x4...which most likely isnt exactly a full 4 inches, but for arguments sake, lets say it is 4 inches....so to me, it looks like from back of bleacher to front of bleacher, to me it looks like you could fit 4 of those 2x4's in there fairly easily (even compensating for the overhang)...so you are dealing with roughly 16 inches....a quick search on the internet shows bleacher width is either 10 or 12 inches...both are standard. im 6'1" and from the tip of my knee to the back off my *** is roughly 24 inches....so, from back of metal bleacher to the vertical imaginary back rest with no recline assuming a stander 12 inch bleacher (as a student, i stood on the bleachers all game and dont remember my toes hanging off, plus against the 2x4 it looks like 12 inches to me) so the extrapolated total is 28 inches ...leaving roughly 4 inches of play to add some recline and compensate for even taller people. unless you have the femur is exceptionally long, you shouldnt have a problem...and its not like people sit with knees together with feet flat on the ground....so a person's natural sitting position would only add more room. i would think even with a recline for the back support, i think most men would still have 3 or 4 inches (if not more) of play even with a reclined rail.
i did take some liberties and i have no idea what the actual measurements are, but using an educated guess with a 2x4 as a frame of reference, i think it could be done.
i agree that it would need some justification, but a HUGE selling point is how much more enjoyable your in-game experience would be. also, its not like it would be a MASSIVE undertaking. its adding some aluminum with some brackets a bunch of times over....pretty simple and straight forward. sure, its a multi-million dollar investment, but one that really improves the gameday experience and makes it comfortable for the average joe....and it doesnt hurt that i think some of our older and more wealthy fans would really appreciate the reduction in back strain and pain that goes along with sitting for 3 + hours in the sweltering heat.
i might be totally off-base on my estimations, but just looking at it as explained there is some room to get it done for sure.
i also doubt it would happen anytime soon, but it would really launch our in-game experience to the next level....screw chairbacks, just give us something to lean against. i still think the temporary chairbacks look terrible especially considering they are left out in the elements for nearly 9 months and are sporadically placed. not a huge deal, but it makes the stadium look unkempt.