The "user data" (comments, posts, votes, etc) that would be available to a hypothetical instance owned my Meta is already public for anyone, so not much we have control over there. "Defederating" essentially just means "blanket banning" a bunch of users at once.
We're aware of the pact and will cross that bridge when (or if) it ever really happens. We're certainly no fans of Meta (or Reddit,or Twitter). So far it seems more likely to affect Mastodon than Lemmy/Kbin.
True, but if Meta (or anyone) wanted to "directly" get that data, it would be as trivial as setting up an instance on something as small as a Raspberry Pi and subscribing to a community here. We would have no way of knowing who it is or stopping them. Defederation is a tool to prevent brigading, not lurking.
If (if) Meta wanted to set a lemmy-style platform, preemptively defederating from it would be a largely symbolic gesture. Doesn't mean it's not worth doing, like I said we'll cross that bridge if and when it becomes relevant.