I've done a few comparisons here and there.
I'm definitely interested in the forthcoming review, especially as I don't seem to be hearing these the same way. I own both the SUI and KAEDE, and to my ears the difference between the two is extremely subtle. I certainly wouldn't say the KAEDE I own is significantly brighter than the SUI. I hear less glare in the highs on the KAEDE, and in fact the KAEDE may actually have even more impact down below than the SUI (which the SUI didn't really need in my humble opinion). I still feel both Flat4s are among the most impressive ear-monitors I've ever heard when it comes to sheer detail extraction and rendering micro-dynamics. Both have a very heady presentation to my ears, with a tremendous sense of inner depth. There's also a distinct lack of nasty resonances which makes them very listenable despite the somewhat bright tilt (especially on the SUI). Where this IEM really intrigues me is in its ability to be both highly resolving and analytical, yet effortless and non-fatiguing. It has a somewhat unbalanced presentation, yet it still possesses refinement and isn't offensive.
It's like... one of the most "fun" detail monsters I've ever heard. I could just gush about it line after line.
Personally though, I don't think the KAEDE is worth double the price of the SUI (at least how I'm hearing them) unless you're a collector or die-hard fan. The woodwork and presentation on the KAEDE is just stunning.