It is not currently on Netflix in the US, it is on Amazon instant, albeit in 4x3 and clearly taken from the video master.

Since it's Paramount, Olive is possible. However Paramount dumped most of its catalog (and almost certainly The Keep with it) with Warner and it definitely seems like a title Warner might be interested in, maybe through the Warner Archive. It'd be awesome if Arrow got a crack at it... who holds the rights to it in the UK? Paramount as well?

I've heard rumblings about a new HD master being made a few years ago. It'd be great if Mann was involved, but it's obviously not a priority for him, I don't know if he's even talked publicly about it since before its theatrical release.

Speculation aside, it would be really nice if someone in the UK were able to record and capture it the next time it appears on Sky.

Glad that there's interest in this title.