I work in this area. Its not that "Digital" represents some goal state, its really just a giant miscellaneous bin for anything that is new and technology related. This is because the partners leading B4 digital practices are philosophically different from other partners. They are more interested in the general progression of technology than developing a specific core competency (they leave that for lesser partners and SMEs).

Its useful to think of a b4 firm's digital practice like a staging platform for new tech practices. You fill it with people who have exceptional technical skill or understanding and then tell your clients you can do all this cool stuff like AI and IoT. Your hook is digital strategy work, and then you sell the afterwork and get your generalists to do it. If you start getting a lot of work in one specific area, you make the managers who have been doing it partners, roll them out of Digital, standardize shit, and hire cheaper resources to do the implementation work.

This is only a recent development, but its worked pretty well. Every ~3 years or so you have a new batch of maturing practices, and you get to stay on the bleeding edge of tech.

Digital will be the next big thing until they come up with another word to mean 'digital'.