The root doesn't "track" or follow its clients; it broadcasts to its entire coverage area with every packet. That being the case, the only limit on client mobility within a single cell is the fact that the client obviously cannot leave the area of coverage.
Different issues obtain when you wish to have clients roam from one cell to another.
A Vivato panel uses directed beams rather than simple broadcast and does indeed track its clients, so you would have an upper bound to client mobility if you were looking at that product.
