i think someone said this already, but what makes the most sense is sony offering disc based backward compatibility and free digital downloads of ps1 and ps2 games as a part of the playstation now subscription. just like how they offer free games as long as you are subscribed to psn. this would boost the subscription rate for the service and offer value to people who don't have fast enough connections to stream.
and remember, the people who write emulators on pc have to reverse engineer everything. at sony, software engineers can work with the actual people that designed the hardware to get the emulation figured out. considering this, the ps4 should be more than capable of emulating ps1 and ps2 games at high resolutions.
But that's throwing money out for So y if they enable disc based BC, I can still find many PS2 games dirt cheap here instead of buying digital