Originally posted by Funkydude on WowAce:

Some form of AltPower support for target/boss frames will need to be added eventually. This was used on bosses In Cataclysm (e.g. Nefarian/Onyxia combo) and is being used again on bosses in WoD (e.g. Ko'ragh). Being able to see them is important for the encounter to know when the next phase is close to arriving.

Something along the lines of what you do with the druid player frame (double power bar) might be the way to go.

Additional comment from Talyrius:

Some bosses make use of both power bars simultaneously. This is especially true for encounters where players themselves have an AltPower. It's useful to see your group members' AltPower as well (e.g., an encounter where you blow up or become mind controlled with a full bar).