BIMserver is supporting IFC4 almost since the final version was released. We have the option to store data as IFC2x3 or as IFC4 and transform the data between the two versions. So far our users have not found IFC4 very useful because it doesn’t seem to add value to practical usage. Nevertheless IFC4 has some great improvements. The guys from Areo (not in any way affiliated with any of us) have written a great blogpost about this. Although some of the claims they make are not backed by facts (yet) we think it is worthwhile reading and we are happy to share it with you: http://blog.areo.io/ifc4-is-it-ready-yet/