There is always a new biggest integration opponent. I don't know who it would be right now, but I could easily imagine France if Marine Le Pen becomes their next president.
Germany has benefited from being able to be a swing voter in the council votes due to QMV. With the UK gone it will now have to nail its colours to the mast if it wishes to resist significantly more redistributive and socialist policies supported by the southern countries, instead of acting as a decider knowing what the UK will do. This could change the politics in Germany in unpredictable ways.
