Well, I am a chartered town planner working in that profession, so may meet your criteria as one with some genuine insight. The first sign of which is to recognise that planning is only one of a number of partly related but largely independent hurdles any development must clear in order to proceed, along with financial viability, land ownership, structural considerations, etc.
I have said much of this before, but to my mind the Whitehorse Lane end represents the best option for further expansion, should there prove to be demand. I say this because the dwellings behind that stand (flats, I presume) do not appear to have rear windows, and are a reasonable distance away. Whether or not that was done deliberately to facilitate development at selhurst, it has that effect. I see little reason to presume that a proposal to build a mirror image of the Holmesdale would be refused, subject to the usual requirements that palace pay towards infrastructure etc. The obstacle there would be working with Sainsbury's, although we have previously discussed the possibility that the club has build-over rights.
Mostly, development of the Whitehorse makes the most sense because it would provide the biggest capacity increase. We would go from some 2000 seats at that end to some 8000.:
The Arthur is far more tricky. For one thing, I can't see a tall structure like the Holmesdale being approved there given the proximity of the houses and effect on light and outlook.
Even if the club was able to buy all the houses on Park road so as to demolish them, planning permission would still be required. Furthermore, it would not likely be forthcoming unless the club could at least build replacements elsewhere. This is not simply a matter of maintaining council housing stock, as at Wooderson Close. It is to do with not losing housing generally. There is a chronic shortfall. Whatever one's view's on the cause and best strategic approach, the fact is that increasing housing numbers has been hard baked into the planning policy of successive governments. In London at least, you can't just knock houses down, even if you own them.
Plus, the Arthur holds some 9000 people now. If we built a mirror of the new main stand we'd only get an increase of 4500 seats. Not nothing, but not the same degree of uplift as the Whitehorse. Add in the difficulties associated with the houses and it all points towards the Whitehorse as the next focus.