If those trends hold, it will be the first time the SVP loses ground since several decades, right ?
Yes, that's right. The SVP has been on the rise since 1991. Since then, they have increased their vote share from 11.9% to 28.9%, and their strenght has gone hand in hand with the decline of other minor right-wing parties and traditional centrist parties. It seems the party has reached a ceiling now, but if they manage to remain above 25% that's still very impressive for Switzerland.
This link offers a detailed overview of previous elections with some maps.
http://www.bfs.admin.ch/bfs/portal/de/index/themen/17/02/blank/key/national_rat/parteienstaerke.html
Can you list what the acronyms stand for on the left? I can't see SPS there, and beyond the main ones I'm having difficulty finding what they are.