It's becoming increasingly common for already-released PS4 games to patch in PS4 Pro advantages after the fact, and the latest to join the fun is Bandai Namco. Detailed in the latest patch notes for Dark Souls III, version 1.11 of the game will introduce support for PlayStation 4 Pro, including improvements to the game's frame rate.
What's interesting about the frame rate boost is that the notes simply state it "increases" when played on PS4 Pro. Whether or not this alludes to keeping a consistent 30 FPS at all times or a boost to 60 is not yet known, though presumably it will be easy to tell soon enough once the patch is live. A Dark Souls III community manager described the frame rate post-update as "variable," so perhaps the game will simply utilize the extra power of PS4 Pro to intelligently boost FPS to whatever possible, whenever possible.
Beyond PS4 Pro the update is fairly substantial in its own right, with new PvP maps Grand Roof and Dragon Ruins being added in addition to substantial item and weapon rebalancing, including buffs for Heavy armor and weapons. There's also support for the upcoming DLC "Ringed City" being enabled, a part of the game's last expansion slated for March 28th.
The Ringed City is $15 alone or $25 with Dark Souls III's season pass, with the new patch scheduled to go live on the 23rd and 24th of March per time zone and region. You can read the full patch notes on the game's subreddit here.