That wouldn't be feasible.
The area between 6/7/8 is where the stairs come down, and losing that would create unnacceptable bottlenecks - the platforms aren't particularly wide, and this would require one set of stairs to platforms 7/8/9 and another set to a narrow island created out of 5/6/empty one by 8. It's also a listed building, and although the actual railway itself has exemption from planning laws, this doesn't apply to all parts of a station.
The empty bay next to 8 would be of little use if it were to be reinstated as a bay, as there aren't many terminating trains from the north. However, 8 is needed for Harrogate line trains, and there is nowhere to put that bay on the eastern side.
Reinstating the bay next to platform 1, and the one beside that where the bike racks are, might be feasible, but I'm not sure what purpose it would serve - they aren't that long (platform 1 can just take 6x23m vehicles as I recall) and not sure that there is a demand currently. It could also create more crossing moves across the station throat, which wouldn't be ideal.
As acknowledged (A new stair access could be constructed outside the main shed on platform 9) where they're is ample room. Obviously this may require a few of the rooms on P9 to be configured. At the moment footbridge access to 9 is via 6,7 & 8. This would simply make it the otherway around. Planning shouldn't be too hard considering it would improve views through the station.
Whilst 6 would become an island platform, at least they're is no-need to relocate lifts as well since these are already provided separately to a subway that is also accessed by stairs. Already it should be wide enough for new steps on both sides of the footbridge straight down to platform level.
Although ideally P5 could take use of where the through lines were lifted in the 80's and be pushed outwards to make it about as wide as P3 opposite. Although this isn't necessary its something I would like to see done anyway.
I do have an idea of how Harrogate services could be shifted over to the Eastern side of the station which is in the thread: 'How could you build extra platforms at York?' started by Meerkat on the 29th September 2020.
https://www.railforums.co.uk/threads/how-could-you-build-extra-platforms-at-york.209665/ Although for this suggestion, that wouldn't be necessarily as Harrogate services could simply be used in P8 with 6 and the adjacent disused bay next to 8 making up another through platform instead.
This particular suggestion is basically about creating one more through platform through the main shed so that P11 could be removed to allow P10 to be lengthened to the same length of P9 opposite, oh and have direct level access from P10 out of the station.
The purpose of reinstating the bay adjacent to P1 is to move the turnback services from P6 or P7 so that either of these could be made into a through platform. Lengthening this shouldn't be an issue although it may mean a few car parking spaces are lost on the Eastern side of the station.
Regarding crossing conflicts, ideally these do want to be addressed although this would be better if it was done at Colton Junction that is quite happily surrounded by fields. Don't P6 & P7 services have to cross the throat anyway, just that this is done when departing as opposed to arriving ?
www.york.gov.uk
