I wanted to provide constructive criticism that I think is very important to the overall gameplay and feel of the vampire line/feature.
On live it is typical to stay at stage 4, because the costs are reduced and the downside, health regen decrease, has a negligible impact on combat due to the abundance of heals that are much greater than the regen. This is not an opinion on the state of health regen - personally I wouldn't mind having it be more useful, but this is just how it is currently.
The issue with PTS changes, is that it makes that problem more exaggerated. Since the passives are tied to hunger stages, and the only way to have all the passives is to be at stage 4, then I feel like I want to stay at stage 4 even moreso than before. A notable difference is that your fire vulnerability gets reduced as you feed. Perhaps this is useful in particularly difficult situations involving fire damage that requires optimization. However in general, most don't consider the fire vulnerability a deal breaker, and would probably still stay at stage 4 to actually have more fun as a vampire.
On live, I occasionally feed to stage 3 for appearance's sake, but I know I'm taking a (albeit small) "hit" to my performance. If these PTS changes go live as-is, I will never feed again. Why give up those passives? Maybe stage 4 sneak speed is niche, but it's fun and good for Thieves Guild, and stage 3 required for the Undeath damage mitigation is pretty good. The reason this bothers me, is because if you had to pick one thing vampires were "about", it's feeding on blood. Yet, the way vampire gameplay works in this game, we don't feed at all; many of us are basically not blood drinkers, period. As far as specifics go, for one thing, past Elder Scrolls games did have vampirism that worked in a similar way, but some key differences are that the fire penalty was much larger at higher stages, and NPCs became hostile to you at stage 4. Both these things may, but probably wouldn't, fit well into ESO being an mmo.
Bottom line: players with vampirism mostly don't feed, PTS changes make that worse. Feeding is essential to the fantasy of playing a vampire. Please consider other ways of tuning the feed scale with more trade-offs.