So, does anyone know if the +3 sec thing means 1 tick or actually 3 seconds? If it's actually 3 seconds, then with enough haste or mastery we should be able to get endless DoTs. If it's only 1 tick, it'd still be possible in theory, with 53.8% mastery.
Edit: above math was ignoring procs from Vampiric Touch. Including those, we get a mere 33.33% mastery needed to reach endless DoTs with the 100% crit proc.