The new boost mode - coming soon in the 4.5 system software upgrade - opens up the power of the Pro to unpatched base PS4 titles. - Eurogamer.net
It does not, ESO is already updated for the PS4 Pro, Boostmode only "boosts" games released earlier than the PS4 Pro (November 2016) which have not yet recieved Pro-patches.
Examples are GTA 5 and Bloodbourne, these games get a small (GTA 5) to impressive (Bloodbourne) boost in terms of framerate(-stability).
The promised Pro-features however in combination with a 1080p-only screen (better shadows, draw distance, water reflections and ambient occlusion) are not at all working correctly and I'm still waiting for a developer statement.
The framerate however, regardless of the TV-resolution you use, is drastically improved on the Pro.