This "thimble" is a mere protection for oil pump, in order to prevent that some larger particles can not be sucked in. Main job is on centrifugal filter, although, today's oils have additives which dissolve preety good carbon deposits and resins that can occur over time inside the crankcase.

Also, it is possible to fit some oil filter, using engine head cover with oil inlet/outlet, the same which has been used to fit oil cooler.

And Foisix, it can be useful for engine hygiene to bring end of the engine breather hose somewhere under the seat (no dust there). I used a filter from my bike's SAI system, and put it on the end of that hose.