Some folks are saying it might become a new location for the Rainforest Café and ESPN Zone, to open up the current area to be used for the new 4th Hotel. This will allow the Monorail station to be part of the new Hotel and blends into Downtown Disney directly. But that is forward thinking.
But House of Blues was designed specifically to be a music venue, and nobody is interested in leasing a large auditorium, so Disney has decided to tear it down to be able to have a blank slate for the future. The permit was filed to just demolish the property. No request was made to build something new yet.