It seems a bit premature to be reccomending rfing to 4 now if the vast majority (???) of kids can't get there with the current options. My kids are all 35 plus pounds well before 3 (I actually take that back I think ds#3 *may* have been a pinch under 35 at 3 but he'd maxed out the height in his marathon and EFTA) so I'd think there might be more danger of misuse if there aren't really any options to get most kids past 3. I think my 35 pounder has maybe 1/2 inch left rearfacing in his EFTA but he of course is over the weight limit. If we don't have seats to accomidate him (at 2.5 mind you, which is not anywhere close to 4) some parents might still put a child like mine in a 35 pound seat because they have room in the shell, or a tall torsoed kid who is under the weight limits but over the shell limits because they heard "you have to rear face until 4". Or like in my case it just seems so over the top to be making a reccomendation like that when my kids will seemingly never get anywhere close to that (even though I desire it) that it seems so "out there" that people can't see how they can/should (not me) comply. I like the "rfing until at least two" motto with a 'as long as possible ultimately reccomended' at least at this point until those 40/40 plus pound seats become widely available AND there are ones that are actually tall enough to accomidate the say 30-50%ile kids to that weight.
I appreciate your concerns, especially given that you had children who might not be be able to RF much past 2.5. I agree that people might wind up leaving kids in their seats beyond the limits. I know that plenty of people leave their kids in infant seats that they have long outgrown until age 1, then put them in forward-facing seats. I definitely think there is precedent for people using outgrown seats to keep up with recommendations that they actually misunderstand.
That being said, I personally don't like the idea of saying RFing until at least 2 and then as long as possible. I've already seen this suggestion made to parents, and I feel like a number of parents consider 2 to be the new RFing safety goal. I know each parent has to make a decision including many factors for when to FF, but there is no research to show age 2 as a good cutoff point for when to FF. When the "until at least age 2" phrase is used, a number of parents wind up prematurely FFing their kids, because they will think 2 is a cutoff point for when to FF. It's just like saying until at least 1 & 20 pounds: parents will turn their kids as soon as they hit that milestone, even though they can still be RFing, and saying at least 2 will cause the same issue.
Since the vast majority of 2 year olds and even 2.5 year olds can already RF in seats on the US market, mentioning age 2 in a RFing recommendation does not provide an incentive for manufacturers to increase their weight limits or height limits to accommodate bigger kids. There would be such little demand from parents if that were the goal, because most kids can already be accommodated to 2+ years. Making age 4 the goal age (and maybe even ages 4-6 based on Swedish research and bone ossification issues) would give manufacturers a reason to change their seats, if parents were demanding seats be available to meet the recommended safety guidelines.
Even taking into account only the seats currently available, most kids can make it to age 3 RFing. By weight, over 80% of kids should be able to RF to age 3 in at least 2 brands of carseats currently on the US market (the Radian & True Fit models), no matter their torso height. 40-50% of kids would also make it to 4 years old in these seats before outgrowing them by weight. My own daughter, who is definitely not short-torsoed, made it to age 4 years and 1 month, 41 inches, and 35 pounds RFing (so 71st percentile for height and 47th percentile for weight) in her Marathon before she outgrew it by weight with a little bit of height left. So even a Marathon and other seats of similar shell height can still accomodate a decent number of kids.