In my experience, GAs are inconsistent in inviting those "who need more time" to board first.

I have taken advantage of pre-boarding, traveling with my family May 06, to board first (though just me to install the car seat, and yes, I did not hold anyone up in the aisle; mom and baby boarded after everyone else).

For any friends that travel with their babies, I advise that they both buy a seat for the baby for safety and convenience (harder now that UA charges 100%), and also let the GA know when they get the gate that they would like to pre-board, and hang around the gate.

In our experience, when we let the GA know we needed to pre-board and stayed around the gate, the GA would let me go through, THEN make the call for pre-boarding, and then UGS/FC and so on. That was the best way.

If the policy has truly changed (and it was not a rogue GA), then that would be a shame.