[jameal]

The author makes the point that "frontend designer" may not be the right title, so perhaps "UI developer" or one of the other titles he listed is more appropriate.

So I don't think he's talking about making designers learn implementation. The point is that the scope of frontend development has expanded so much that it makes sense to split responsibility between "front of the frontend" UI responsibilities and "back of the frontend" responsibilities like managing state, cache invalidation, routing, etc.

In any case the line between design and dev turns gray when you consider that designers can't practically mock up designs for the web for every viewport size, define what every micro interaction looks like, etc. There are so many nuances to creating a great UX that it makes sense to have a class of front end devs with those kinds of proficiencies.