Twitter blocked links Mastadon for a hot minute calling them spam or unsafe or something. IIRC they backed down after a couple of days. Reddit has already been getting shit press for the last couple of weeks, tech journos are watching this all unfold closely, is Reddit dumb enough to take an action that is blatantly censorship and anticompetitive? It would be totally unspinable.
If they do that, it'll tell you a lot about reddits thinking here. Spez current position is that the people complaining are a small minority and this will all blow over soon. If Reddit really believes that, then they best course of action is to let the complainers post their Lemmy/Kbin links, avoid a fresh round of bad press, and the lemmy/Kbin users will be gone in a couple of weeks and the reddit user base will remain largely intact. If Reddit views the risk of a mass migration to be a real and existential threat to their business, despite what they are saying publicly, then blocking Lemmy/Kbin links would make sense as a last ditch effort to keep their user base of casual users ignorant of popular alternatives, bad press being a necessary cost worth paying to try to retain the user base they need to sell for their ipo. All for that assumes Reddit is behaving rationally though, which Spez has shown isn't a safe assumption.