Data point:
We attempted to board ORD-OGG on the 788 a few weeks ago with our infant son in hand and 3 F BPs.
Contrary to some other stories upthread, after consulting with the cabin crew, GA determined the infant would not be permitted in a F seat at any time during the flight, except on our lap (consistent with the posted rules). Our son's ticket was cancelled by the GA and we were permitted to board with ontheJR as a lap infant. Though we were cool with everything (knowing the rules upfront), the GA brought a supervisor over none the less who was very apologetic.
ps though the UA website shows no bassinets in 788 F, there appears to be one at seat 1A. We had 1DF and were permitted to create a makeshift bassinet above.
