The patch notes state that they're lowering the passive mana regen and increasing the mana regen from relics so I'm assuming you won't notice too much of a difference if you're already consistently make use of the relics. It seems like its aimed at bruisers but it will hurt APs the most, at bot lane anyway.
Outside of a few exceptions, AP's bot will typically lose relic control to bruisers. You can't really contest them for it because depending on who you're up against, you risk dying or losing a large portion of your health.
I usually end up farming under my point denied of the middle relic and my own relic near me because all it takes is one phage proc to put me in a dangerous situation. So, unless I happened to pick up an Athene's, I typically end up mana starved with barely enough to push the creep wave back while the bruiser continues to push none stop because they aren't reliant on their abilities to push fast. They also aren't nearly as easy to gank and kill whereas most APs and AD Carries bot are just fodder. Of course they probably have a bit of Life Steal as well since it's really cheap and investing in WoTA as an AP really hinders your damage output unless you got good bases making any harass you do manage to land in safety negligible as it's easily healed by the Life Steal and/or their control of relics.
As a primary squishy player, I feel naked without armor yellows, Veteran's Scars, and the 3 points in Hardiness so it's not like I can make use of mana regen seals or the 20% increase in regen from relics that you must put 9 points in utility to reach(Runic Affinity).
AD Casters, bruisers, w/e you wanna call them. They give no ****s about mana because once they get one damage item, they're perfectly capable of auto attacking an AP to death.
I'm not sure how it will effect the other portions of the map but this is a nerf for most APs bot lane. Maybe a slight buff for APs everywhere else, I dunno. I will need to see how all of this plays out with the new items and of course the S3 new items and changes as the latter aren't too far off.