A "well placed source" close to Eurogamer told them that the PlayStation 4 may receive an update to natively emulate PlayStation and PlayStation 2-era games. This is different to the streaming, cloud-based emulation service, PlayStation Now, which will provide backwards compatibility for PlayStation 3 titles.
Our information suggests that the same internal emulator strategy is planned for PlayStation 4, and we understand that Sony is actively pursuing the ability for older titles to run without the blurry upscaling seen on PS3, suggesting that native HD resolutions are being targeted. Assuming this intention carries through to final code, we'll be seeing an effect similar to the resolution scaling seen on unofficial PC emulation of Sony's consoles, as well as a great many of the "HD remasters" we saw on PS3 - where original assets were rendered at a higher resolution, often without any actual remastering at all.

If true, you may one day soon be able to purchase and download classic PS1 and PS2 titles to your PS4 hard drive and play them some some rather crisp looking textures and visuals.