I think until the cartridges are no longer available, they won't be available on the eShop. Moreover, it will probably be another generation or two before we see DS eShop games. Even GBA games generally don't show up on the 3DS eShop, and many of those have been out for quite some time.
I also don't think there's enough of a public desire for those games to see re-release yet. RBY were old, and they were also the best-selling games, as they were available when the Pokemon craze was at its height. They tie in well with the 20th anniversary, they were GB games (which already get sold regularly on VC), and the code was probably simple enough that allowing wireless trading wasn't that hard. For the 4th and 5th gen games, the public desire isn't there, and without servers for wifi, Nintendo probably wouldn't want to re-release them (although one would think that some of the existing gen 6 server space could be used, perhaps...). I suspect it'll be at least 5-10 years before we see 4th and 5th games re-released, and I'm dubious that it'll happen in that time frame.
