As per last update of SA:MP, we got access to GTA VC Map in SA:MP
I've recently seen a video in which a guy has merged GTA 3, VC, SA, 4 and 5 maps in GTA SA and provided links.

I was wondering can it be possible to integrate installation of map files with 'installation of open.mp'? 
So everybody who uses open.mp will have full access to those maps without making one person having access to map by installing it manually.

It would be cool to integrate all maps and use it as multiplayer just by adding that map mod addition along with open.mp

Having DL features such as downloading models is in our roadmap, so yes, it will be possible, just the way samp 0.3DL works