I'm not sure you're really understanding the implications of this mod and you keep changing what you think this mod would be good for. You've claimed it would help with accuracy and timing as if the way to improve accuracy and timing is to give people the option to not lose as many points while getting 50s on every note in a drain section. You've claimed it would be good streaming practice...can you even fail during a stream without missing any notes? Even with nothing but 50s the map would need pretty high drain, I'd imagine. You've claimed it would be a good mod for high bpm and high AR and I don't know what you meant by that at all. High bpm makes it harder to get non-300s if you can play the map and if you can't you'll be getting tons of misses anyway...and high AR makes a map easier unless you can't read it, in which case you are again getting tons of misses. Now you claim it's good for maps with high cs, which is pretty much absurd. If the circles on a map are too small for you, you're going to miss them and this mod wouldn't save you.
If you're incapable of passing a map, that's what nofail is made for. That covers any and all reasons you can't pass a map, whether it's because the cs is too high, whether it's because the map is too fast, whether it's because you can't read it, whether it's because your accuracy isn't good enough to make it through the drain sections, etc. The penalty for not being able to pass for any reason at all is 50% of your combo multiplier. This mod would cover only the case in which your accuracy wasn't good enough (or cases in which you missed enough notes to be left with a tiny tiny sliver of health that drains away before hitting the next note, in which case I don't know how you would even begin to justify having less of a penalty than nofail). Adding this in with a lower penalty than nofail would be to say that accuracy is unimportant and that's just silly because osu! is a rhythm game....or at least I hope we can agree that it's enough of a rhythm game to put accuracy on an even footing with aim or how fast you can move your fingers.
The one thing I think this mod would be okay for (and I've mentioned it already in this thread) is spinners like in Mendes+HR or in happy30 maps. This is because I personally do not believe spinners to be an important part of osu!. They're hit objects that map usually over arbitrary collections of sounds and that you hit with no particular sense of timing or rhythm. Having them be the barrier to passing certain maps seems kinda silly to me. This mod is definitely not the best solution to that problem though. a change in how drain and hp gain work during spinners to lower their potential to cause fails would be nice...