Like jeans, sneakers, what's on your iPod, or the type of iPod you've got, iconic chairs serve as a window into your personality and a way to discern taste (to those who care, at least). The chair, for a long while, has been the iconic mascot of good design--everyone's gotta take a load off sometime, right? Interestingly enough, Alice Rawsthorn has gone so far as to challenge the longevity of seating's authority, of course, after properly explaining its unyielding prevalence.
Will the chair remain as important to design in the future? Probably not. That's not because collectors will suddenly stop fighting over them at auctions, and design museums will start to de-accession them, but because other areas of design will be perceived as equally interesting and important, if not more so.
This is partly because, as design has become more popular, the public's understanding of it has become increasingly sophisticated. People now want to learn more about other areas of design, especially as the design innovations in those fields often have far greater impact on their lives.