LemonNation Discusses Implications of Patch 3.10 on Supports
41 hp off of base hp. 6 armor off base armor. The passive is changed from 1 scaling down to .5 to a flat .75, which means that before 100 souls you get less armor/ap, and after 100 you get more ap/armor. 100 souls is quite rare in a competitive game, so this is basically a straight nerf for support thresh.
These nerfs are very significant, they make Thresh WAY WAY squishier, and should knock him down a few pegs. These changes make it so Thresh will be losing most 2v2′s during laning phase, and he will be reliant on ganks to win the lane (with his lantern making forced ganks viable). He will only be able to fit into comps with strong junglers such as Jarvan who can abuse the lantern.
.5 seconds off her stun duration on her Q, due to a bug fix. This is a very major nerf, and I believe will mostly remove her viability. She currently has an issue of being somewhat weak in lane, as well as having mana issues, but she got past these factors with her bubble kill potential, counter engage, and healing. Making her bubble a significantly shorter stun duration will remove a lot of her kill potential, which will make other supports such as Fiddle, Zyra, Sona, Blitz, Master Yi, Lulu all be higher priority than her.
The removal of the global passive on TF will make TF support not as viable as support. I expect that he will still be a common pick in competitive play, but we might start seeing him as a mid laner rather than a support.
Aegis/Locket was nerfed fairly significantly for junglers and tanks, since a lot of the self stats on the items have been removed. This means that if the jungler builds Aegis/Locket they will be significantly squishier in Patch 3.10 than they have been in the past. However the active and MR aura is still incredibly important for the team. This will make it more likely that it becomes the supports job to build the Aegis/Locket, rather than the jungler, since the self stats are not as important for a support.