I think there's a strong possibility of a G/S remake. I'm not going to mention all the hints from D/P, because loads of other people have already done that. =/ You can look at it a couple of ways. A G/S remake could be for fun, just to let all the older players enjoy playing in Johto once more, and to improve the storyline and difficulty of it. A lot of the people on here are saying there's no need, because all of the Johto Pokémon can be transferred to D/P/Pt. Oh yeah... That's from using Pal Park from the older games. What fun is there in that? I don't want help from R/S/E and FR/LG to finish my Pokédex on the NEXT generation. I already caught them on those games, why can't I go somewhere new and catch them again in the current generation? Besides, with the DSi, Nintendo are going to focus on those who actually go out and buy a DSi, and a DSi has no GBA port, so no Pal Park. How would we get all our older generation Pokémon now then? By including them in another game so we can catch them, then freely trade between DSes. G/S remakes would be the solution to this problem. My bets are it being announced early in 2009 and will probably be released in 2010. This will close off the 4th generation, like Emerald and FR/LG did with the 3rd. And then Gamefreak are free to start working on the 5th and possibly last generation.
I'd absolutely love a G/S remake. I played Gold for ages, and would love to do it again. But it needs serious improvements... Especially Kanto. As much as I loved going there, it was incredibly easy. I have to say though, it must be quite difficult programming 16 gyms and fitting the right level requirements. But... We'll have to see how it goes. Let's all keep our hopes up.