The DPC summarily rejected the complaint in July 2013, pointing to the Commission's finding that the Safe Harbor principles followed by Facebook were adequate.
Schrems sought a judicial review of the DPC's decision from the High Court of Ireland in October that year, and in June 2014 the High Court referred questions about the case to the Court of Justice of the EU.
In his opinion, Bot said the DPC should not have used the Commission's ruling on the adequacy of the Safe Harbor principles as an excuse to avoid hearing Schrem's complaint. Despite the ruling, national regulators should be allowed to determine such matters themselves, he said.
The CJEU's judges have just begun to debate that and other matters referred to them. Their ruling, when it comes, will be binding on the the Irish High Court.
Schrems is pinning his hopes on Bot.
"It seems like years of work could pay off. Now we just have to hope that the judges of the Court of Justice will follow the Advocate General's opinion in principle," he wrote upon reading the opinion.
Sign up for CIO Asia eNewsletters.