UA announced that it would take about a year to complete the switchover and the announcement was made last June. The update looks as though it's progressing apace. Remember, E+ is actually a hard product swap and needs to be FAA certified, not just a matter of boarding a new menu item.
Golds were free to select E+ at time of booking. Silver's likely SOL on this configuration because they can't select E+ until T-24. But, that's not unfair.