potential of Star Engines+Flat Out+Cruising Speed = 42" in a turn
Star engines and flat out both prevent any other voluntary actions that turn. And as such you get to use 1 or the other. Since flat out is better you no longer can use star engines until we get an faq that directly alters this fact. Meaning a total movement of just over 29"
The same is unfortunately true for DE vehicles with aether-sails, the sails work in the movement phase but prevent any shooting, If you can't shoot you can't move flat out. So in both cases your speed is locked at just over 29" And we have 2 useless vehicle upgrades.
The next useless vehicle upgrade is the Holofields since without a roll on the damage table for glancing it will have very little effect all game.
vectored engines are almost as pointless as well since only a lucky penetrating roll will make the upgrade have any effect. You have more chance of been glanced to death which will circumvent the upgrade.
Spirit stones are also weaker, Glancing hits will not cause them to be any use, and the few times you take a penetrating hit it will be modified to a point where SS have little or no effect. A single penetrating shot only has a 1/6 chance of activating the stones, And when the stones are active you still cannot shoot at your full BS. Meaning all they allow you to do is move flat out. You may as well save the points.
By my estimation all fire prisms got 45 points cheaper, and all wave serpents got 10 points cheaper in this edition.
Wave serpents are still by far the most effective and durable tank for the eldar. The reduction of ST means the tank is always at an advantage over the more expensive battle tank variants, And the twin linked guns give improved shooting V/s anything that requires high numbers to hit. While your unlikely to place anything other than shooting units in a wave serpent, the range and mobility still gives a solid tactical boost in a lot of situations.
The best way to keep a Prism safe now is range, Using that range to stay out of range of the multiple shot guns will keep your tank trucking for a few turns at least. But be aware outflanking and deep striking shooting units will probably destroy the prism before it gets to retaliate.
DE got the harsher end of the stick by a fair margin, Even with the range reduction there wargear gives they still will find themselves in range of most shooting and glanced to death very very quickly.
Warp spiders for me have had a surprising boost in tactical effectiveness. Since eldar are now going to struggle to deal with a well dung in shooting army the spider fill a role that swooping hawks simply cannot match. The durability of the spiders, matched with the speed they move at, and the ST of the guns they carry mean these are going to be needed to take out Hydra's and basilisks on the board edge. Hawks could do it in assault but since they cannot assault when they arrive, and the fact the spiders are faster mean that spiders are far far more effective. They also have the added advantage of armour and been able to dive for cover when they appear after shooting first.