Can't speak for SLAB, who has made his disdain for Kross pretty clear but the thought of a 3-way between 3 of the best workers in NXT with a hot feud/angle going on and Finn vs. the current monster is more on the lost potential vs. the "well that's going to suck" end of the spectrum.
But hey, I get that probably Kross and Scarlett are main roster type talents and they probably want to move them up to prime time sooner and as much as I love Finn, Cole and KoR they are probably best served staying in NXT where they can work awesome matches and not let their size become a deterrent so NXT can simmer that.