To me it seems that SuperCell is trying to gear the game towards the use of dark elixer troops at higher levels. Specifically in small numbers rather than masses.
I think a Phoenix that has the ability to be reborn would play well with the strategic direction SuperCell is taking the game. When the Phoenix dies, it turns back into its egg form and if not killed by defenses, it will be reborn. I won't provide detailed stats because this would take extensive balancing but the concept is a good one in my opinion. The Phoenix can't be too overpowered but if used correctly they could be very effective. I personally like the idea of having to deploy my units strategically. A healer can be invaluable if used properly with giants. I think SuperCell should add more units that have this capability, especially since towards the endgame attacking becomes quite difficult. At town hall 10 there's so many defenses all dealing considerable damage, adding units that can soak up a large amount of damage allows for strategies that focus on surviving rather than rushing to get whatever it is that your after. It's different to the Hail Mary we see now with hog riders or balloons + minions where it's try to kill as much before dying. Feel free to improve on my idea in any way in the comments.
Another idea with the pheonix could be that once he dies, he provides a burst of heal to x number of tile in a radius (from where he died). I think it would diversify attacks some between flying/ground units and introduce another healing type unit to the game.
