Hi,
If you have performances issues, please report to us right now, don't wait for 1.8
Unity own internal system will always be beneficial as a side effect to all Addons. there is a but...
"but" currently, I would be very careful with the first few iterations of this new core. I strongly doubt it will be more efficient: it will be more portable, yes, that's the primary goal of this core change, efficiency isn't really the motivation for this...
So, I personally don't really expect any good news just yet
Unity is under a lot of pressure to provide support for IOS submittion before february 2015, so performance is secondary on that front too... unfortunatly, compatibility is the real problem currently.
Bye,
Jean