My understanding is that the EU PSD2 regulation indeed is supposed to make banks adhere to a standardised API. That being said, I wouldn't expect a super easy to use REST api with documentation powered by readme.io.
There are however some inititives for open API standards that might be accepted by a majority of the banks.
That's obviously and opportunity for Teller, Figo.io and other players, they can perform legit aggregation just swapping out their scraping for bona fide API access.
But the situation is more complex... even banks can become aggregators for other banks if their customers want... These are interesting times.