With all the latest references to the Johto Region, (some being Professor Elm being mentioned when you acquire the Happiny egg, Jasmine appearing in Sunyshore City and the Pokemon Contest Master Rank, and as if anyone could forget; the TV show that opens the game, talking about a red Gyarados) the to-be-followed trend, with Generation III releasing Generation I remakes, (meaning if it is a trend, Generation IV could hold G/S remakes) and several other things that people have spotted, it can only be assumed that a remake is very much so possible. However, I have a feeling that with no official word about it, (or as far as I've heard) it will very likely come 2009/10 time, seeing as Platinum will release sometime this year, in Japan. Of course; if it is meant to be that there will be remakes.
Though they did well to shield Platinum so close to its release. Maybe they're doing the same with the G/S remakes...?
But to fully answer the question, it is not officially known that remakes will be made, alongside the Fourth Generation. But in the same sense, Nintendo have not shrugged it off and said there won't be remakes. So its pretty much in a deadlock, until official information is released.