I'm curious about this as well. I think actually that if tested, safe, and doesn't impact the install at all-wouldn't this be better than a toddler boot? But, if people see this in use perhaps they will use other items to prop the seat up. Which leads me to saying how would either impact the safety of the seat? Ie/ what if we had a high density foam piece. Not safe? Do you think that it might become allowable such as pool noodles to achieve a good rf angle for a seat?
A few thoughts on this... 1st one being, the Radian is really the only seat out there that wants to over-recline in many vehicles. If you bought a Britax or Evenflo or Cosco/Dorel - you get the picture, you'd be either fine, or you'd be having to add a pool noodle to get the seat sufficiently reclined. (With the exception of vehicles which have flat and super firm backseats - but most modern vehicles don't have perfectly flat back seats.)
Over-recline of a seat is rarely a problem - with the exception of Radians. So parents really never have cause to worry about getting a seat more upright. Not in the vast majority of cases anyways.
People get creative now in terms of plywood and 2X4's and you-name-it. It is amazing the types of things you see at public seat checks. So I don't think that this will really give rise to any new DIY inspirations. For one most seats don't need it so it would be a useless idea that was counter-productive to what they were trying to achieve, and two - anybody who is intent on going-their-own-direction in regards to an installation is going to do it anyways. Whether it be rf tethering in a seat that doesn't allow it, using an infant seat ff'ing, or whatever random thing you want to throw out there.
Misuse is rampant out there, and some of the things you see are things that are unbelievable - until you see them over and over. So do I think this will give people ideas they haven't previously had? Nope, not really.