I imagine the 'new 300' will be Airport to Gyle, current 36 route Gyle - Morningside, current 38 route to Cameron Toll, Terminating at the bus stance.
I can't see how this could be possible because as I said above, Slateford Station is facing the wrong way for to get to Craiglochart Avenue where the 36 goes. So it has to go via Slateford Road. It COULD go Ashley Terrace mimicing the 38 but again, this makes no sense as theres several new hotels (either built or being built) at Fountainbridge which I can't see Lothain wanting to miss out from the airport which makes me believe it will continue that route until it reaches Earl Grey Street.
I do wonder however if the 300 could go up towards Morningside from Earl Grey Street which would give the people of Brunsfield and Morningside a direct bus to the Airport and Gyle then to Grange/Blackford, or via Melville Drive towards Dalkeith Road.
Either way, it's going to be interersting to see how they run these new routes.
I do have to say however that I think it might be very confusing and perhaps it was bad judgement to have the 35 coming back again so soon after being rebranded to 300 as some folk are used to seing the skylink bus and assuming 300, and goes to Ocean Terminal... So many other options such as 28 which could have been used instead.