Existence of the technology doesn't guarantee that it is scalable by perhaps an order of magnitude.
Judging from the literature I've seen, Brightcove's live streaming offering is actually Akamai. It seems a little like putting all of one's eggs in one basket.
Well, obviously I am not going to convince you. Suffice it to say, when DirecTV's cloud DVR has problems, it won't be because they couldn't scale it up, but rather someone made a bad decision to artificially limit that scaling. Akamai isn't the only game in town either.
AWS Elemental MediaLive
Live and On-Demand Streaming | Azure Media Services
All the hard work has been done.