I'm not big on UV
filters, but I can't fathom how a cannister filter can replace the function of a UV
filter. UVs kill bacteria - cannister filters don't. The two thing are totally different beasts, with different functions.
Activated carbon, or any of the other synthetic resins on the market remove "organic matter and proteins", so there's nothing new about the Opti-Carb stuff. Even if you used it, I wouldn't suggest losing the skimmer. Again... different things for different functions.
No big deal removing water from the tank during water changes. It's only detrimental to the fish if you're not watching and suck one up in the siphon tube!
The new Fluval G6 is definitely a pretty sexy unit. I'd be lying if I said it hadn't made me think of ditching my HOB
Marineland cannister, but the price tag is a bit much for me. But if I had a sump (I don't), I wouldn't even be giving it a second look. It's just a cannister filter with some fancy features and what appears to be an easy method of changing chemical media. It's not going to replace UVs and Skimmers.
I haven't heard many good things about the Coralife Super Skimmers. For about 1/2 of what you'd pay for that G6, a better investment might be a better skimmer.