It's way too early to be complaining about nerfs. It's way to early to be complaining that "ITC has it out for Tau" (which is demonstrably false). In fact, I would suggest it's way to early to be complaining about literally anything that we see because it is largely without context. We just got stat lines today, but we have no idea if they are good or not because we don't know what weapons do (we will find out tomorrow) and we do not know what the new overall rules will be.
As for Riptides, they are too strong and have been for awhile. Most armies do not bother shooting at them because they are too tanky. Most major tournaments see people running the Riptide wing in non-Tau armies because they are that good. Getting nerfed isn't a problem (although it doesn't feel good) and understanding how the nerf works within the entire framework of the game is important to consider too (IE, Tau get nerfed but other units get nerfed as well *Cough Warp spiders Cough*).
TL;DR: Pump your brakes guys, the game isn't even out yet.
As for today's announcement, this is great news. Custom movement speed for each individual models allow for more flexible balance. Most people I know were upset that Guilliman could only move 6in in the movement phase for 7th edition. This makes it really difficult for him to get into close combat, where he excels. 8th edition gives him a 8in movement range, which is a great improvement. In fact, I would wager that most "close combat" units will likely by in the 6-8in movement range.
Vehicles losing AV and hull points is huge as well. This can give the potential for under used units to see some more action. Things like Dreadnoughts could make a comeback, and even the piranha might see more use. It will undoubtedly make Hammerheads more of a solid choice because you won't have to worry about it getting popped early from lucky shots. This could give rise to a vehicle resurgence in the hobby.
At the very least, the meta will be shaken up, and that is what is most important here.