XSS and marines structures are terrible in every test round I've been a part of so far on both Xeno and Marine sides.
It reinforces even more defensive gameplay from both sides and even more long played out sieges to occur, which is slow and boring as hell. Defensive game play at such a large scale offers nothing interesting in terms of gameplay when both sides are just sitting behind their respective barricades/resin walls waiting to see which side fucks up first by getting bored pushing out. Turrets will be spammed due to the low cost and ability for any engineer to place them easily. Every single test round has been a slideshow due to the lag caused by said turret spam among the other various issues that occur during testing, both lowpop and otherwise. Flame turrets cause more FF than damage to Xenos. The Ordinance changes to MT are a step in the right direction from what I've seen externally, but haven't had the luck of rolling it myself as of yet because everyone dogpiles it on High every time a test is announced.
The core formula of CM is a good and fun thing. It works for the most part. Turning it upside it's head with such a drastic change in game play and all heaped into a single massive update isn't necessary. There are existing mechanics that could be improved or worked on piece by piece to still keep things fresh and new so we're not doing the same stale meta strategies over and over again, which will just become even worse and mind numbingly boring if/when this update has it's issues corrected and is merged into the official branch. You thought ABC was bad? XSS will replace it times a hundred.