Mastering is not the only domain where WaveLab is used. For quite sometimes, WaveLab has been oriented “processing in the box”, ie. without external hardware.
Hardware i/o like external gear, prevent multitask batch processing of course, a domain where WaveLab has a strong implementation and popular usage.
Still, the popularity of WaveLab has incrementally reached standard studios, and now there is more demand for hardware support. Especially, Mastering Studio try to have their distinct brand, their sound, using combinations of devices. This is how I see things. Therefore I think WaveLab will have to provide this kind of support, without, of course, ever giving up on multitasking batch processing (without hardware).