Perhaps Emperor Ferdinand II dying in 1628 before enacting the Edict of Restitution would be a satisfactory POD. OTL’s Ferdinand III had not been elected King of the Romans at that point but was King of Bohemia. In TTL, Ferdinand III might be willing to make concessions to the other electors to get their votes in the eventual imperial election.
Ferdinand III was more pragmatic than his father and would be willing to make religious concessions to the imperial princes in exchange for increasing the powers of the emperor. Of course, Wallenstein would be a wild card in this TTL. But if Ferdinand III was able to advantage of the strength of the Hapsburgs at that moment to increase the emperor’s power, than the Empire would certainly be more unified by 1700.