Serious workloads is very inefficient without a proper windowed desktop environment combined with a Finder and a Terminal that can access files across all apps.
Also, having an x86-compatible CPU at the core enables high enough performance for virtualbox/vmware, which is a huge enabler in that it allows running windows or linux VMs side by side (or even integrated) with the native desktop.
A converged ARM-based Macbook sounds very much like a toy computer; a facebook+youtube media consumption station with an option for perhaps doing limited creative work such as composing an iMovie or touching up some photos at the most.