imho. one of the primary factors that makes a Sampler popular is the available amount of libraries it has going for it. Since Halion 5 has so many great features. It is just natural to see more sample libraries offered for it, by both Steinberg, and Third-Party sample developers.
Take a look at Kontakt, if they did not have all these third-party libraries available, since NI licenses Kontakt to third-party developers, Kontakt would have not been what it is today… It is surely very popular because of the abundent, high quality sample libraries it supports.
Now, back to Halion 5, and Steinberg. Halion 5 is a fantastic sampler, but lacks the sample library content that Kontakt offers, so … solution is : Steinberg needs to move their behinds, and begin making it attractive for third-party sample developers to use Halion 5 to develop new, diverse, and high-quality libraries for it. They have to start somewhere, and this is a good time for Steinberg to get the ball rolling. Otherwise, I don’t see it flourishing to its real potential.
Hopefully Steinberg will be wise, and take Halion 5 to the next level … Namely : Offer Lots of libraries (both themselves and via third-party developers).