I believe the only limitation keeping them from deploying them nationwide yet is that they have a shorter range than traditional WSR-88Ds. This would essentially mean that we need more radars nationwide, which is an issue in mountainous areas and is also a funding issue. Unless they can find a way to increase their range to be comparable to the WSR-88Ds, they will need to secure enough funding for the additional PAR sites and space them perfectly so as to limit the number of radar holes.
Other than that, the advantages are very significant. NWS meteorologists can scan specific sectors instead of the entire atmosphere, which significantly improves scanning speed, which increases the chance of NWS meteorologists catching quick spin-ups, which is a huge improvement in QLCS situations.