In nebula4 everything will be the same. An acqua plug-in will be ALSO a skinned library, so a library for nebula4 too. In nebula4 you can have skinned or textual libraries. In general skinned libraries will feature more instances inside, bundled in a single product.
An other benefit of skinned libraries is the auto-sample-rate feature. Loading blue eq you will have at the same time 44.1, 48, 88.2 and 96 Khz. Nebula4 will load the proper library, depending on your actual sample rate. At the moment nebula3 can't do it. But an acqua plugin is already doing it (acqua plugins are featuring the same engine you will find in nebula4)