It is desireable for a raiding rogue to Envenom immediately after a deadly poison tick. Doing so every single time you envenom is actually a large increase in dps. This is extremely hard to do while paying attention to an actual encounter. So I'm requesting a mod, i would make it myself yet I don't know how. It's displayed like a swing timer or castbar. (I'm thinking quartz at the moment) It waits for a deadly poison tick and then starts the animation (the bar goes from full to zero in 3 seconds.) That's really all it needs to do and it would provide raiding rogues with a simple UI to help maximize DP damage.
I'm currently working with another author (Tifi) on a combat monitor addon that shows tick timers for any dots that you cast or proc, along with a few other things. Keep an eye on Eventhorizon (on Wowinterface), next update will have what you need.