Shouldn't it be possible to convert the map files from SA to V?
Apparently they already managed to import a big portion of the map into GTA IV.

Hi there!

Could anyone please finish the GTA Berlin mod?
The project has existed since 2002(!) but there hasn't been any activity within the last 12 months.
The team has created so much content, it would be a shame if everything was lost.

Check out the GTA Berlin website:
http://gtaberlin.de/en/news.html
Also have a look at this Google image search:
https://www.google.com/search?tbm=isch&as_q=site:forum.gtaberlin.de
Isn't that impressive?