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I imagine we won't get the WoTC designer take on this until we get the DMG 2. However, I've been playing with this as a monster template.
Largest issue I see right now is hot adjudicate a rage daily power when it is deployed on a monster.
I have fiddled with several ideas:
1) Leave it be and transfer it straight over
2) Have the rage sustain on a minor
3) Make the rage work like other daily powers for the purpose of a template, that is, work for only the first active round.
Rage powers are built to be flexible in the timing of their use. As a player, operating with a limit on the number of rages you have at your disposal per day, you need to choose which encounter(s) are worth using one of your rage powers in.
Monsters have no such dilemma. Monsters almost always participate in exactly one combat encounter, so choosing which encounter to rage in is no longer an issue. As such, there's no real reason to keep it coupled to the use of a particular power. Templated monsters are elite anyway, so why not do the following:
Give them a daily power of your choice as you would normally when applying a class template, but remove the rage portion of the Effect line. Give the monster a separate, always-on ability identical to the rage effect. This represents the monster raging at the beginning of combat, and allows the DM to not have to worry about whether or not that monster has entered into a rage or not. The daily power is still quite strong in terms of sheer damage output (which may be increased by the rage's effect), so you shouldn't feel like you're gimping the monster in any way.
For instance, if you wanted to give your 1st-level Elite Barbarian monster the Bloodhunt Rage power, you would give him a daily attack power that deals 3[W] + static damage and half damage on a miss (call it Bloodhunt Strike), and then a separate ability that grants the monster a damage bonus when either it or its target is bloodied (call it Bloodhunt Rage).
Alternatively, do the above but instead of giving the monster a daily rage attack power, give it a single use of the Rage Strike power (with the appropriate damage expression for its level). The monster should still get a separate always-on rage ability.