Well he helped created the first computer networked workstations, practically invented Object Oriented Programming, created the concepts of overlapping window management...
... I struggle to think of what needle your trying to move that wouldn't be moved by any of those.
His insights about this field and its potential, narrowed by his views that many of today's computer engineers have forgotten fundamental principles and practices of old, favoring instead popular trends of new, and that the Web was built by amateurs, I imagine, would yield a very interesting subset of ongoing work.
Although my IDEs are quite powerful, they are yet far from the Xerox PARC workstations experience used to feel like.
My tablet, even a Surface, aren't as easy to use or programmable in the same way as the Dynabooks were envisioned.
So yes, he is still relevant, because mainstream computing is still catching up to his vision.
EDIT: from a brief read of his wikipedia page:
"Kay has lectured extensively on the idea that the computer revolution is very new, and all of the good ideas have not been universally implemented."
Coming from someone with multiple major accomplishments (OOP pioneer, smalltalk, overlapping window GUI, etc.), that's a powerful message that can still be applied today.
Namely; much of the low hanging fruit has been ignored and much of the world is in a technological stagnation.
Separately they could be made to sound pessimistic, but together there is much reason for optimism.