Update: the end of last week I was on JFK-LAS and got upgraded to F about 36 hours out. Woke up to a nice upgrade email from Delta. lo and behold I check the Delta app and I have that dubious pre-select entree button. Well I clicked it and I was able to select a meal for both myself and companion. We enjoyed the burger... nice meal. This was a 737-900ER. So perhaps Delta has worked out the kinks... here's hoping.