Why will it lose it's challenge? You're only not getting attacked by friendly NPCs, there is still the 100% weakness to fire and the major weakness to the Sun. If you want more challenge up the difficulty and/or stop being OP and gimp yourself like no enchanting or smithing or whatever. Stop complaining over nothing unless you're just complaining to relief stress. If you are then in does matter what I say.
You don't get it. Vampirism isn't suppose to be an all fun power-up with no drawbacks. There should be many benefits, yet there should be drawbacks. And the mob of angry villagers was one of the most significant of these. It was great to run around the towns in the dark as a blood-starved vampire with the villagers chasing after you.
Now that experience is taken away. And for what? Because the Vampire Lord gets attacked when he shifts out? I honestly think Bethesda shouldn't of removed the 4th stage effects. I am confident they did it to appease the other people who kept complaining about being attacked. If they hated it, then they should of cured it.
With blood bottles and new feeding animations, it would be twice as easy to revert back to stage 1 without needing to sneak into a person's home. But Bethesda completely changed vampirism. I hope it will be like Oblivion, then. People refuse to talk to you in stage 4. You get more powers such as "Reign of Terror" and other things. The eyes and appearance should be the same.