The notion of defining an area of design is ultimately unhelpful. In doing so however one achieves useful purposes.
For a student of design these new definitions, such as speculative design give validation to work that they thought wasn’t viable. Students are scared to leave the confines of their own field, these fields are defined for them by their degrees.
Graphic design is normally commercial in nature, or if not directly commercial, it uses the methods, outputs and tools of its commercial cousin. There’s no reason for this to be true, but history, industry and tradition reenforce this opinion. Areas like speculative design validate different ways of working. The name alone combines an intelligent way of thinking with the word design.
This kind of work has been open to a graphic designer for a long time, there may even have been times in the past when this kind of work may have been more possible than it is now. Speculative work is something people have been making long before it was labelled. Fine artists, performers, sculptors etc have been creating work like this. Those fields have had a much easier time in the last 100 years (since Duchamp) to redefine freely what their practice means.
Defining fields of critical practice is both liberating for some, giving them permission to work in non-commercial manners, but at the same time it creates a new box. Having work that is labelled as speculative design is one thing, but once labelled a speculative designer are you then expected to only make work belonging to this camp.
All work produced by an individual is associated in some way. It is a troubling thing to define an individual, troubling even to define a single piece of work as belonging to a school of thought. It is impossible to capture the broad nature of anything in this way.
It is worth asking, who is the definition for, the artist/designer, or the critic/writer/spectator. The latter initially feels sated with a definition, but it only serves to shut down conversation, put a full stop to further thought and discussion.