I dont think the ds games had the memory to store all the data for all the trainers and maps for all the regions.

 

Such Pokemon hack of all regions will never exist, sorry to say that. Here are some reasons:
1. Each region is powered by different game engines(reactor, scripts, etc.), if you're planning to 'smash' the ROMs together.
2. Making it out from scratch 'is' possible, but will eventually take forever(like years you could say).
3. Aside from the hacking issue, Nintendo will never release such Pokemon game due to their marketing purposes.
4. No one hasn't decipher the map hacking of Black/White, so it's impossible, for now.

I'm pretty sure that there are more reasons that why this kind of hack will not exist.

 

Well, it does fit in with reason #2 from my previous post. The point of that reason was to show how tedious creating the hack will be.
Cobalt Blue project was started in 2006. The last update announcement that Blazichu, the creator, made was around 2008.
During that process, there were high amount of bugs, crashes, and glitches (such as no Wild Pokemon appearing), in the attempt of creating more regions.
Yes, Blazichu did promised Kanto, Johto, Hoenn, and Sinnoh, but as of now, Kanto and Johto regions are the only regions that are properly working(Since it's from the original Gold ROM).
Sorry to say this, but those kind of hacks are something that might not be accomplished.

 

Is that so? Never heard about that hack. If this is true, well all I can ever say for you is to wish that Luca J S will finish that hack. Hopefully it 'will' be one of the first all-region Pokemon hack, but I wouldn't count on that.