In reference to Proposal #1:
To start with, I'm curious as to the reasoning for wanting to eliminate the possibility of minibikes being modified to complete in offroad classes. I'm assuming that this applies to enduro classes.
There are already class designations based on engine displacement; I don't think there should be further or additional limitations regarding wheel or frame size.
There was a 14 year old kid who rode his first AMA enduro this season (a National). He is a very fast and skilled rider, short in statue. I believe that he rides a CR-85. He finished, which was a great accomplishment, and even beat a lot of the adult riders. He likely would have not been able to ride this event if forced to ride a full-sized bike.
I think the proposal for a 19" minimum rear wheel is perhaps an oversight, and not considering that some full-sized off-road bikes come with 18" wheels (Note: I believe that YZ's (and all MX bikes) come with 19", not 18", rear wheels.)