Re: how to activate notification LED?
I'm afraid there is some confusion: what you're seeing is not a notification LED (since the Lumia 730 does not have such an LED); what you're seeing is most probably the proximity sensor InfraRed LED, used to determine if there's anything near the surface of your screen (directly on top that sensor) - it's the one that turns your screen off during calls.
So, no, it can't be activated (since it doesn't exist).
It will not come with Windows 10 Mobile (for the same reason).
And, for the arrival of Windows 10 Mobile, no specific release date has been announced at this point, all we know is that it should arrive towards the end of 2015 through early 2016.