I can't speak to the German side, as I'm not particularly familiar with it, but I think they would still have to move through Belgium to some extent. France had fairly substantial fortifications and the terrain advantage on the Franco-German border in Lorraine. If the Germans attack through their wouldn't they run into essentially the same issue the French did going the other direction in 1914? Plus, German military theory was heavily reliant on the idea of envelopment. To me, that seems to motivate for a swing through Belgium to envelope the French armies like they did in 1914. However, in 1911 the French were still using Plan XVI, not XVII, which was much more defensive in nature. It also gave more weight to a German advance through Belgium and allocated, IIRC, 7 corps to the Belgian border to counter a German advance. I don't believe Plan XVI envisioned an offensive into Lorraine at this point, as that concept emerged only in Joffre's later rewrites of the plan.
As a fun sidebar, ITTL if/when the French shift to a less visible uniform it won't be OTL's horizon blue ones, but the "Resada" style that they trialled in 1911 and 1912 but abandoned when there was an outcry against abandoning the red pants... So the French would be wearing green and brown, not blue!
I agree, they would probably still go through Belgium, but possibly only south of the Meuse.