The proof is that he wouldn't have supported any adaptation directly, just as he was hands off with LOTR adaptations after he sold the rights.
The proof is in the fact he sold the rights, no?
We're literally talking about whether he would get involved with a massive revisionist adaptation of his work, and we know he wasn't even favouring that for LOTR and ended up selling the rights entirely. How are you spinning this to imply he would suddenly be involved in adapting the appendices?
Sure, no one knows either way because he is dead, but we're talking IF he were still alive right? There is no concrete proof and evidence for the discussion of speculation, so I'm not sure what you're even asking for.