Yes I wanted to try, because I thought Unity would be faster as my engine is not 2d, more 3d engine. But Unity isn't that much 2d, and you have to fake things to have it 2d friendly. So It takes me some time to adapt my engine to handle 2d better, but it's be more reusable.
Moreover, Unity debugging is just awful, and I'm wasting more and more time debugging simple things that I master in my own engine.
Also, Unity offers possibility to go to iPhone, but my engine is not that far from working on OpenGlEs2, so it's not that far from iPhone/Android, if needed.
So Unity seems a good option at the beginning: you can have something running very fast, and it looks promising ! But when you dig a bit deeper, it is full of undocumented things & weird behaviors. you can pass through, but it asks you hours. Hours that you'd better spend in programming the game than hacking an 3rd party engine.
The port should be quite fast, because I already did it once