If you are using a pass, you’ll have more freedom in Switzerland and Germany, because there aren’t any reservations required. In France, you’ll need reservations on TGV and Intercity trains.

It depends what you want to do, but a few days in Switzerland, seeing Bern and some of the mountain passes might be nice. And then travel up via the Black Forest and Rhine Valley?

Grenoble is 2 hrs by local train to Geneva. You could also consider a stop in Lyon - which is a great city with wonderful food. Or a trip to Chamonix, in the shadow of Mont-Blanc - then continue into Switzerland.

Another option, if you don't want to see Germany, is to spend your time in Switzerland and Austria, and then get the excellent Nightjet from Zürich, Basel, Vienna, Innsbruck or Munich direct to Utrecht.

I did this last summer (absolutely loved Utrecht!) and took the sleeper down to Vienna.

I remember taking a train from Lyon to Aix les bains that was absolutely stunning. It was going through mountainous terrain and bordering a few lakes. Then close to Aix les bains you're pretty close to Annecy which is a very pretty city on a lake too

(it might be not exactly on your way, but that's not too far from Grenoble )