As they said they would late last month, it appears Electronic Arts have gone ahead and uploaded some of the source code for the Command & Conquer Remastered Collection.
Dropped onto GitHub recently is a new CnC_Remastered_Collection repository, containing plenty of code for both the original Command & Conquer Tiberian Dawn plus Red Alert. Properly done too, with a GPL3 license to go along with it. They've attached some additional terms with it, which the GPL3 allows, to mention things we would expect like not giving rights away to trademarks and such.
Why did they do this? As they said in the original announcement it's to help the community for things like modding and to "ensure compatibility with projects like CnCNet and Open RA". While the free downloads of the classics have been up for years since EA set them free originally, this is another great step. If it goes well, hopefully EA will do this for other classics. Even if it's not the entire package, it can really help game engine recreations.
While the Command & Conquer Remastered Collection which releases on June 5 won't officially support Linux, there are the CnCNet and OpenRA projects and both are quite popular. Big fan of OpenRA myself.