Why not...for kids nowadays it is "normal" to be in a carseat, harness, booster seat, whatever much longer than when I was a kid. When I was 12 if my mother put me in a booster I would have put up a fight because "no one else was doing it", but today...its the "norm", so why would my 8-12 yo think that there was anything unusual about sitting in a booster.
And to all the short adults/small adults I most certainly think their should be some type of adjustment to be able to be made to the seat because 4'9" is 4'9" whether you are 8 or 88...the seatbelt won't fit you properly.
For the ones that worry about the too long legs, just watch a toddler sit on the floor with their legs totally flat on the floor, knees bent and feet in the back. They are extremely flexible at such a young age, that sitting criss cross in a rear facing seat really is no big deal.
Very happy the recommendations are official and hopefully states will be on top of this and change their laws