I'd love to see the C&C games come to GOG but I really doubt they ever will, or at least they're as likely to as Starcraft or some other Blizzard game is to show up here. I say that because the entire collection of every C&C game ever made - "The Ultimate Collection" regularly goes on sale several times a year for $5 and includes 17 games including expansion packs. It's been packaged like that for years and I imagine it is the best selling item as far as C&C products go, and a better deal than buying any of the games individually.
GOG sells some multi-game pack collections but not as a set of 17 games so if that collection were to be offered up to GOG they'd likely want to break it down into smaller groups of games in multiple packs if not right down to individual games. No matter how one sliced it, I highly doubt GOG would sell it for $5 on sale like it is sold now for years for the entire collection. If they did it would be without any precedence.
But, the collection of C&C games is huge and spans a great long period of time from the oldest to the newest game in the collection. More likely than not if any of the games would be offered, they would be individual games and probably only the oldest games. They're very well liked games and so they would probably not only be sold individually, but at a high price because they'd be very high demand DRM-free for the first time in digital format here. I bet they'd go for $10-20 each regular and go on sale here for $3-5 or more. While there are people here who would be happy with that, I think a lot of people would balk at it and cry unfair that the DRM-free GOG versions are like $5 each on sale but the entire collection is available on Origin on sale for $5 even though it isn't DRM-free.
Can't say it's impossible because nothing is impossible but it seems incredibly unlikely to me that EA would even remotely consider doing that. If it were to happen though, whether piecemeal or as a pack and whichever at whatever price, it would be a step in the right direction at least, but I doubt it is very likely.