Allowing users to send and receive BTC via the site / app would give them a shot of relevance into that under-30 crowd they are losing the war with versus Twitter. Would do wonders for the user adoption and thus price eventually for the currency as well.
I am pretty sure that the under 30 "crowd" makes up the vast majority of the userbase of facebook lol. I see very little to no reliance to facebook accepting bitcoin. The only potential positive to this would be if they were to accept bitcoin for payment for the sale of ads.You would think so. However, the main user of facebook games are women between 40-55.