Hi Marko, it's a common problem that we face too. What we do is just follow the QDF proposed solution to handle that, but in addition you can use Git LFS to handle your binary files (Gitlab has 10Gb free for that purpose)
Some useful links:
QDF Integrated Development Environment (IDE) here they use SVN but you can apply the same principle to Git.
Hope it helps,
Merge on QS file is not possible. Don't know if you have reviewed WIP from www.ebiexperts.com? It's a comprehensive lifecycle management solution for QlikView and Qlik Sense files.