Yeah I think Slack's updated stated internal policies are about as reasonable as one can hope for from a tech giant, if one can trust them to stand by those policies. Your article was on my mind when writing this, I guess I should have linked it.

The crux of the matter is whether you can trust a big tech company to do what they claim they will. They all think AI is worth infinite dollars. In that world, without some very clear, painful, straightforward, contractual penalty ... well we've seen that the tech giant plan is that rules are meant to constrain your competitors' behavior, not yours.

If they wrote "If any of your data is discovered to have been in an AI training model, Slack owes you 10x your lifetime payments to Slack, and any involved whistleblowers get 1% of the total paid" in their terms of service, which means if Slack screws this up, the company is immediately bankrupt, that might prove effective. But a promise in a "privacy principles" policy that doesn't appear to actually be incorporated into the core ToS does not have a lot of teeth.