B) as far as I'm aware, everyone else is running Linux, except maybe one of the CDNs, but I don't know if that CDN is actually running appliances.
However, everyone and their uncle are launching a streaming service in the next 18 months, some of those might get enough traffic to justify appliances, and they can take Netflix's work here to get a competitive box off the bat.
Also, at any point, one of the current big guys can say "hey, netflix gets 200gbps from one box, why do we have 4? Why don't we try FreeBSD on some of these"
CDN appliances are pretty isolated, so it doesn't matter as much if most of their proprietary stack isn't ported. Chances are, they've got someone on staff with FreeBSD experience, and FreeBSD experience ages better, because there's less churn.
But (a) what other streaming services even have CDN appliances, and (b) of the ones that do, which are using FreeBSD as a base?
If none of Netflix's competitors will use this patch, then it makes no material difference whether they share it or not.