I have made this point before, so apologies for repetition.
A capacity of 40,000 could certainly be achieved if the right deal could be done with Sainsbury's.
As can be seen from an aerial shot of selhurst, there is a large enough space between the pitch and the houses on Whitehorse Lane to replace the current stand and supermarket with a mirror of the Holmesdale stand. The Whitehorse Lane houses do not have back gardens or, I believe, rear windows, and so would not be impacted.
A project like that would replace the current 2300 capacity stand with an 8300 capacity one, an uplift of 6000. Selhurst will hold 34000 after the new main stand is finished, so there's 40000 seats overall.
Of course, Sainsbury's aren't just going to roll over and say yes, and they certainly aren't going to just disappear, but I wonder if perhaps a project like that might involve us building them a replacement store under the new stand. It's not Impossible.
The Arthur is a very different matter. As poor as it's facilities are, it holds 9500 already. Even if we replaced it with a mirror image of the new main stand, we'd only get an uplift of 4000 in capacity. Hard to see that paying for itself effectively.
Plus, there are far too many houses far too close on Park Road that would have their light and outlook decimated. There isn't a reality in which that doesn't matter or can be overcome. Perhaps, if we were a champions league regular, we could look at buying them to knock them down and replace them, but it would be fraught with difficulties. Some sort of compromise renovation of the Arthur makes more sense.