All good choices, though I have a few more that I'd personally add.
-As someone already mentioned, the 'Dune' games would be awesome in HD with a new engine, especially "Emperor: Battle for Dune".
-'Krush, Kill, and Destroy". I have a soft spot in my heart for this whacky series. It's basically Command and Conquer meets Fallout meets Mad Max, but it's aged badly due to old graphics and old RTS controls. Would love an HD remake of these games.
-Universe at War: Earth Assault. This game still looks good, I would just love to see it re-released so it gets more attention. I'd argue it's one of the most underrated RTS games ever.
-Rise of Legends. I'd really prefer a full-on sequel to this one, as the game's campaign was its weakest element, but this game was so creative and fun, with incredibly interesting and varied factions that were totally different than the usual fantasy tropes of knights, elves, orcs, etc. Would love to see this one out again.
-Myth and Myth 2 (already mentioned). These games were so freakin' good, and so far ahead of their time, that they still hold up pretty well today, but a graphics overhaul would be so much fun. Just make sure to keep the same narrator and music.