Udyr is on his way to being the new Sejuani

Riot, you're repeating the same mistakes you made with Sejuani with Udyr. He has been essentially the same since I started playing this game back at the end of 2012, a few changes here and there, like removing the mana regen from turtle stance, but this is the first time I remember seeing him being a decent meta champion. And so far, its been because of the introduction of Runic Echoes, which has become a problem item for several junglers. Namely Nidalee, Elise, and Gragas. The problem is, Udyr is the only one of the Runic Echo junglers in the meta that is receiving straight nerfs because of synergy with the item, in addition to nerfs to the item, without receiving any compensation buffs. Heck, Nidalee recently was "nerfed" for being toxic to the game and warping picks and bans, even at the competitive level, and she received compensation, which actually made her a faster jungler. This is the exactly the same thing that happened to Sejuani because of her synergy with cinderhulk. She was continuously nerfed because she was good with the item, then nerfs came to the item, and she was never compensated, and fell to a nearly unusable state because of it. She's starting to reemerge recently, but it has been nearly a year.

The way you are going with the Udyr changes, with the inevitable changes to Runic Echoes, either removal like its predecessor, or future nerfs, in addition to the Udyr nerfs, like the ones on the PBE currently, you are going to push him into obscurity.

The current PBE changes:

Base Health Regen lowered to 1.2 from 1.742

Phoenix Stance (R) 
    Damage per second lowered to 10/20/30/40/50 from 15/25/35/45/55
    Third hit damage decreased to 25/60/95/130/165 from 40/75/110/145/180.

Eventually when he falls out of favor, as well as runic echoes, his base numbers will be so low that the only option will be to go Tiger Udyr because Phoenix will be too low to go pure tank, and Tiger is the only stance other than bear to have not had it's numbers hit. If you really want to push Runic Echoes Udyr out of the meta, a few suggested changes would be to flat out remove the bonus movement speed from Runic Echoes, nobody actually needs it. It would hopefully take away the incentive to build it on him, and junglers like Nidalee, Elise, and Gragas do not need it. Then a compensation buff could be done to Udyr to fix his numbers if people stop building the item on him. Another suggestion, which I've felt would have been good for a long time, would be to change his turtle stance to scale off of health or armor instead of AP, which would further remove the reliance on Runic Echoes.

TL;DR They're nerfing Udyr like Sejuani was, for being good with an item, while nerfing the item, which will inevitable remove him from the game, unless compensation buffs or number changes happen.