why not put service valves on way to fixture or PEX back to supply
with valves?

currently my bathroom has hot and cold service valves in basement,
individual valves for sink hot and cold and toilet

as part of a general upgrade I am thinking of PEXing everything
seperately with a manifold and ball valves in basement.

this way running sink or flushing shouldnt effect shower like it does
today and service much easier.

the built in stop valves only help for washer replacement, anything
more than that your turning off all the water.

myself I would go with individual ball valves, perhaps with rear access