Valve has made a booklet with information about and around the Steam Deck, and in it there is quite a lot of information. Anyone who worries that today’s Steam Deck will be a one-time story can hopefully breathe a sigh of relief when Valve outlines a product that will span “several generations”. Gaming on Linux noted the following as written by Valve:

"Steam Deck represents the first in a new category of Steam handheld gaming PC’s. In the future, Valve will follow up on this product with improvements and iterations to hardware and software, bringing new versions of Steam Deck to market.

The information is not very concrete, but at least a vague promise that there is more to come. It’s not inconceivable that Valve envisions more frequent updates than console generations.