PlayStation exclusives have a massive fanbase these days and are definitely selling PlayStation consoles. Sony's exclusives on PS4 were particularly appealing to the masses and they routinely made records in sales. Sony games on PS2 barely sold 5 million if they were not Gran Turismo. On PS3 Uncharted and The Last of Us as well as LBP and God of War 3 sold over 5 million while Gran Turismo declined in sales and since 6 hasn't sold 10 million like it used to but overall Sony exclusives became more popular.
PlayStation this gen has made amazing strides in making its IPs more mainstream. They have multiple 10 million sellers this gen, Uncharted 4 is already above 10 million sold, God of War, Horizon Zero Dawn and Spiderman will follow and The Last of Us Part 2 is likely to do so. They have got good public relations except for backwards compatibility which will could be leveraged as a seller for PS5. People already own these games in the tens of millions. Free 4K 60 fps patch with high resolution textures and assets will make them see PS5 as a better value for money and they will buy it. PS5 doesn't just need backwards compatibility but should be the best place to play exclusives on PS4.
UPDATE: Its pretty much confirmed by a Sony patent.
"Each asset such as a texture called for by legacy software such as a legacy computer game software has a unique identifier associated with it," the patent explains. "The unique identifier can be rendered by imposing a hash on the asset, and then the asset stored with its identifier in a data structure. An artist remasters the textures for presentation on a higher resolution display than envisioned in the original software, and stores them back in the data structure with their identifiers.
"The original software is then played on the higher resolution display, with asset (such as texture) calls being intercepted, identified, and the data structure entered to retrieve the remastered asset having a matching identifier. The remastered asset is then inserted on the fly into the game presentation."
https://www.eurogamer.net/articles/2018-10-07-sony-patent-sparks-playstation-5-backwards-compatibility-rumours-again
