HBO and Disney in particular are both large enough to succeed with their own app.
Simply having a back library isn't enough. They have to have a war chest big enough to crank out a decent amount of quality new material, rivaling Netflix's, for many consecutive years for people to begin to take notice.
Sigh. It's almost like your reply isn't even to my comment.
Netflix has the branding (that people understand the meaning of. Yes, HBO and Disney have strong branding, but not as streaming platforms) and the cash stream.
Consumers may not be geniuses, but they can understand that Disney and HBO have video, and that it could be streamed to them. They already had to figure out that they could stream Disney's content from Netflix.
I think multiple giants combining forces (basically to create the original Netflix experience all over again, with a great back catalog and very low prices, but also publishing newer seasons of their popular shows fairly aggressively) is the only viable short-term threat,
The immediate threat to Netflix is that the distributors are not renewing their licenses to stream content through Netflix, whether because they're getting more money out of Amazon or because they're taking it to their own platform, or perhaps streaming is only cannibalizing their DVD sales. Whatever the reasons, Netflix already has to deal with the fact that their library is shrinking.
In addition, there's another clear way they can have their lunch eaten by competitors. Amazon is partway there already: when you watch video on an Amazon Fire TV device, and you have a Netflix subscription, you're offered the opportunity to watch content on Netflix. The next step is to unify the listings into one app, and I predict that Amazon will be the one to bring us that, too. That's going to require giving the user a little more control over search, but they'll still find ways to force recommendations on you — and no doubt, to autoplay them too, just like now, to inflate statistics.