I never heard about that plan, but it's certainly interesting, and I wish it had happened. I remember Moe's appearances on the Mike Douglas Show, and he was still spry. But "Uneasy Lies the Crown" was in 1990, and Moe died in 1975. I can't guess any particular '70s episode where Moe would have fit-in as himself, but Columbo worked in LA, so I'm sure a cameo for Moe could have been done in almost any episode.

I saw that Mike Douglas interview myself, and was equally impressed by how well composed he was. He spoke very articulately, and still looked like the old Moe except with white hair.