Neat find. Are you able to remove the Ring of Hircine and put it back on to use the power again later, or do you need to keep it on permanently to keep its power?
I have been using a different hybrid glitch – described at
http://forums.bethsoft.com/topic/1447673-werewolf-vl-hybrid-glitch-question/ – which requires you to really line things up properly between the Dawnguard and Companions quest lines.
I normally avoid glitches and cheating because I find it takes me out of the story and can often feel overpowered. (Oh man, the inner turmoil I experienced when I found out you could make game-breaking gear with a series Fortify Restoration potions!) In this case, though, I find it just makes the game more fun for me. It's pretty easy to imagine narrative explanations for why my character would do this. After all, he's already conquering every guild, learning every Shout, and accumulating as much wealth and power as possible so that he's strong enough to prevent the end of the world, no matter what the personal cost. Of course he would try to get Hircine arguing with Nocturnal over where his immortal soul should go, and of course he would cut a deal with a vampire to delay that argument.
As for the gameplay ramifications, I don't find it overpowered at all. I guess that's because what you do in your transformed shape doesn't help you gain normal experience/perks, and also because the penalties offset the bonuses. Werewolves can't ever get resting bonuses. Vampires get a ton of bonuses and a ton of penalties that pretty well balance out. (You can opt out of both most of those vampire bonuses and all of those penalties with the glitch I'm using as long as you never feed in humanoid form, but I don't feel like the bonuses you are left with – Vampiric Sight and ability to profit from Necromage – unbalance the game noticeably.)
I could cure vampirism and werewolfism right now and the only real impacts it'd have on my play is that I'd spend less time seeing in the dark, I'd level faster, and I'd lose the option to eat everyone in the room when I get bored of sword fighting. That's a good option to have when you're level 70 and just want to mix things up every now and then.