Rock Band 4 on the PC was something that fans had asked for for a long time. The port of the game had followed the franchise around for a long time, and alas, Rock Band responded by trying to crowd fund the port on PC to the tune of 1.5 Million on crowd funding site Fig.
Sadly, the campaign failed to materialize as Harmonix would have liked it seems. The campaign has now finished at $792,817, around half of what they were looking for. That isn't so good.
Hard to say what is next for Rock Band now, as this doesn't speak well to fan support for the series. We will have to see how the game is supported going forward I suppose.