The issue came up with FII mostly because they went so long without the label letting them record an album, and wrote so much material in trying to get into the studio, that they ended up in a situation with enough material for a double album. I don't think it's as much of an issue now that they write in the studio as needed.
And I'm glad they didn't get to release FII as a double album, because the album is much stronger as a result of culling the weaker material. I'd definitely say the same for IaW too.
This is a very common situation for bands recording albums to end up writing more than an album of material, and the vast majority of the time it's the right call to cut it down to one disc of the stronger material, otherwise we end up with something like Load/Reload, or Use Your Illusion 1/2, which both would have benefited greatly from being culled to one album. The same would have been the case with FII. I also don't think that any album post-SDOIT would have benefited from being even longer.
They've only had the creative need for a double album once since then, and I gather that it still took serious convincing to release SDOIT as a double album, and they were prepared to release it as one disc on the real possibility it wasn't going to happen. It may not have made the label any more open to doing it again in future either, so I don't think they had free rein to do it. Even if they did, just because they could do one, doesn't mean they should do one. Quality over quantity.
~75 minutes of music on every album is already a lot of music to write and record, and on the latest album they felt that even less total album time was appropriate for what they wanted to achieve creatively. If they ever felt the need to do a double album in future, I'm sure RR would be pretty open to it though.