Boomkin threat : Does it hold you back?

[Milky]

Well, moonkin threat has always been a minor issue for me personally. However, I have never gone as far as you have. Although a threat reducing ability would be awesome, we sadly don't have a practical one (yet). So with our current state, you have to do without it.
Some things I'd suggest are: stand at or close to max range when and if possible. That way you need to have 130% threat to actually pull the boss, which is a lot.
Shadowmeld in case you do pull, but holding/chilling dps before you pull would definitely be better for you and your raid. It's not a threat dump, like you said, but it's still a good O#S#!T button, if needed.
I personally don't use my first shooting stars proc if it is too early into the fight, and if I'm at risk of pulling, I don't usually stop. What I do is refresh my dots (even if they're still ticking) and maybe use wrath/starfire opposite of the eclipse state; yes I would have a nice dps drop, but I'm still dishing out some damage and not taking much risk.
In addition, it should be noted that most tanks are prioritizing survivability over threat (can't blame them). Even if your tanks are good in all other areas, their threat might not be as good. Misdirects and Tricks of The Trade are always good, even when well into the fight. Salvation is a helpful option as well.
Another thing which is viable for the time being is to use the reduced threat meta gem. 2% mana isn't better than the threat reduction, especially if you have such threat issues.
If this doesn't work for you, then you might need to ask your tanks to do better.

[Trispec]

Cat Form - Cower

I do this because my spells go BOOM and I'd rather not have the mob do the same to my face.

... in all seriousness I don't do that often. But there was this one time... it saved my feathery hide.

You don't understand why i said RANGED threat drop, do you?