This intrigued me. I'm no expert local, so the following is just musings.
I think this would be a challenge.
I got the idea for this from some of the NSW canyoners on how they plan routes. I can't remember any names, but don't blame them if this is nonsense.
If I were planning on doing this, I'd download QGIS, get topo maps from GetLost (free maps - need Grampians, Fyans, Watgania and Thackeray), and then go to Elvis and get elevation data, reproject it to the same projection as GetLost maps (or vice-versa), then using the profile plugin for QGIS, trace out possible paths. The interesting thing about the profile tool is apart from a height profile, you get slope/angle profile. Which can tell you (within the limits of your elevation data) how steep a path might be. But it's not perfect. For Example, Helicopter Spur approaches 100% slope (1 meter flat is 1 meter up), but can't tell you there's rock bands where you are more or less scrambling. It gives something like 60% slope for parts of Stanley Name Spur (which again scrambling), so it doesn't tell if your scrambling or just a steep hill. I'd probably look at Google Earth satellite data of a proposed path.
But it's something I do for a place I've never been, not sure it helps, because I always imagine I'm up to the challenge, then often find I'm not....And the topo maps/elevation data can't really help with vegetation info.
Using the above, this is from Rosea Carpark to Mt Rosea summit (which I've walked in 2019, so can't be hard The 60% slope near the Grand Stairway might be an error going off track a bit with the path or not, I don't remember

).

- Mt Rosea carprk to Summit Topo

- Mt Rosea carprk to Summit height profile
- SERRA-01-height.png (8.07 KiB) Viewed 7775 times

- Mt Rosea carprk to Summit slope profile
- SERRA-01-slope.png (13.68 KiB) Viewed 7775 times
Tracing a potential path after leaving Mt Rosea summit would be where the fun starts, although as an intellectual exercise, I imagine not so much fun in reality - although I've read people report on Dalton Peak hikes, so there's probably tracks that resemble nothing like the path I traced by eyeballing the topo map.

- Mt Rosea to D'Alton Peak via some bumps (horrible ms-paint stitching together)

- Mt Rosea to D'Alton Peak height profile
- SERRA-02-height.png (11.13 KiB) Viewed 7775 times

- Mt Rosea to D'Alton Peak slop profile
- SERRA-02-slope.png (13.88 KiB) Viewed 7775 times
Anyway, just my musings.