Back in the day I played Boot Hill, Gamma World and Top Secret.
D&D always beat them out for time and creative investment.
I'd like to see both Top Secret and Gamma World again. Boot Hill I can do without...never had the itch to strap on my spurs and six guns (and I think Deadlands/Savage Worlds has that area covered pretty well now).
Of course they wouldn't publish it. People have been trying it from them for years, but WotC prefers to their ****ish ways, sittings on beloved IP to reduce the competition in the marketplace (one of the reasons I feel our IP laws in the US need to be rewritten).