Welcome to the forum.
I have both 1/32 and HO. In HO I have Tomy, AFX, Model Motoring, Mattel/Tyco and Tycopro.
The answer to your question is yes and no. Yes, there are 6" 1/8 AND 15" 1/8 curves coming for Mattel/Tyco. No, they are not made by Mattel/Tyco. They are compatible. The same way the Tomy 18" 1/8 curves are "compatible" but not made by Tomy.
From all reports, the Tomy 18" curves are a perfect fit, so the Mattel/Tyco 15" and 6" should be as well. At least we can hope.
You can see a test photo of both at http://www.jaysraceplace.com/tycoslots2.htm
In answer to the question of what 6" curves allow you to do: You can create a 6 lane track, or a 4 lane track with different radius turns or make type hairpins. You can make better use of small / tight spaces. Make turns that start out tight and loosen up or start loose and tighten up.
Basically, it allows the same options that 1/32 scale plastic track gives you.