In Norway, politicians have promised that they want to go ahead with data retention regardless of the legality of the EU directive. It has been postponed multiple times due to cost and technical issues, but we'll probably get it eventually :-(
Even though they still have a majority in parliament together, the conservatives are strengthened, and labour weakened, and a large part of the argumentation was that the EU "required" it. With this legal opinion I'd imagine at least some people in the labour party will consider opposing it, and more people in the conservative party - it's quite possible they'll find it hard to muster a majority to defend a challenge against the law.
It might actually be better if a high court deems the national law to be just fine, since you might get a verdict in the European Court of Human Rights.