Voracious Wurm enters the battlefield with X +1/+1 counters on it, where X is the amount of life you've gained this turn.
Seeing as this is not a triggered ability, but a replacement effect, would I be able to gain life at my end step with Wall of Reverence's triggered ability, then add to the stack my Wurm's ability to gain X +1/+1 counters? (After all, that's life I gained in my turn.)
The following rules seem relevant here:
603.3b If multiple abilities have triggered since the last time a player received priority, each player, in APNAP order, puts triggered abilities he or she controls on the stack in any order he or she chooses. (See rule 101.4.) Then the game once again checks for and resolves state-based actions until none are performed, then abilities that triggered during this process go on the stack. This process repeats until no new state-based actions are performed and no abilities trigger. Then the appropriate player gets priority.
614.1. Some continuous effects are replacement effects. Like prevention effects (see rule 615), replacement effects apply continuously as events happen -- they aren't locked in ahead of time. Such effects watch for a particular event that would happen and completely or partially replace that event with a different event. They act like "shields" around whatever they're affecting.
614.1d Continuous effects that read "[This permanent] enters the battlefield . . ." or "[Objects] enter the battlefield . . ." are replacement effects.