Also The Thirty-Nine Steps by John Buchan is well overdue a revival.
There's never been a film or tv version of The 39 Steps that was faithful to the book. If I had to pick one, I'd have the original b&w Hitchcock version, with Robert Donat. The Kenneth More one was more or less a remake of that.
It is strange that it was published in 1915 but does not mention the war specifically. It is as if it is set in 1913.
Er - it is quite clearly set in the summer of 1914, immediately before the outbreak of war. Richard Hannay says at the end "three weeks later, as all the world knows, we went to war.... But I had done my best service, I think, before I put on khaki".
Personally, I prefer Greenmantle. I loved it in my early teens, and have re-read it many times. But doing it well would require a lot of location filming, and the reasons why it's particularly relevant today are also the reasons why it will probably never be done. And who would play Sandy Arbuthnot?
*Trollope's Barchester Chronicles and The Pallisers are due a remake. There've been some excellent radio dramas recently but the TV series are quite old now.
But the Barchester Chronicles had Alan Rickman in his first big tv role! Who else could play Mr Slope?