just some sparse thoughts.. naming is hard but we can agree on the fact that in the name, moving from left to right we go from general to particular.

If your module brings to PDL the ability to open websockets then PDL::WebSocket should be correct, but there is also the possibility that you module enhances Mojo::WebSocket with the ability to create live ndarray, so i'd dont exclude something like Mojo::WebSocket::PDL or Mojo::WebSocket::PDLarray

In my opinion this depends on the point of view of the developper and how the module is created: if more stress is put on generalising the Mojo::WebSocket part or the PDL one.

Just my humble opinion

L*