Lorraine had significant iron deposits and the Saar had quite a bit of coal. If France had managed to hold the Saarland (maybe no 1815 territorial cessions, maybe they regain it later) could the Saar-Lorraine area have ended up being France's Ruhr?
The Saar is a german-speaking land, so France might need a strong military force to hold the area. France can economically benefit from Saar but at a significant military cost.
If you want that Saar becomes France's Ruhr, you need a long occupation so the area finish to be almost French.