There's a reason that Tau and Codexarines are Blood Brothers in the ally chart. I'm really not expecting a whole lot of strife, honestly.
I'm really concerned with how the Riptide will compete. It feels like it could easily be a Heavy Support with its firepower... but it's not competing with Broadsides or Hammerheads. Will it be more effective than 3 Crisis, however?
Hmm... It's not that much different in size (in mass it is though, haha) from a Necron Triarch Stalker, which is also Elite. The stalker is really squishy though, so the Riptide with T6 and W4 would be a defensive powerhouse.
But do we know if it has jet packs? If not, it's probably breaking more lore rules than anything so far at Tau's disposal.
It looks to have a LOT of options. Which is inherently a good thing for it. I can't imagine it could possibly be bad unless the base cost is too high.
I don't think you should be thinking "Crisis or Riptide" just yet. They will solve different problems. Depending on the rules, I'll probably end up with 1 Riptide in my regular army and none in my Stealth army (if XV25 get fixed)
Of course, they may just nerf the snot out of XV8 suits because they were the 'spammable' of choice in the previous codex. That's their usual marketing strategy, at least.