Well we know the photos app will feature extensibility so in theory existing plugin makers will be able to update their plugins to be compatible with the new Photos application.
But will Apple offer a "pro" type plugin that gives us the features of Aperture? Seems unlikely.
I don't use aperture, I only use iPhotos. I'm also not a professional photographer.
I think what's likely is Apple making photos a free to use, pay for advance app. Maybe even allow other people to build those "apps" for them. I doubt Apple will ever abandon professional photography as that's one of the bigger segments in the professional community. I also doubt that Aperture became so unprofitable that Apple decided to can it. What's most likely is that Apple shifted resources to maximize the value and decided Photos is more worth it as it can address both pros and non-pros with one sweep.
i also think that Apple DID learn the lesson from iworks and FCPX, which is to not overpromise and underdeliver.