As time goes by, like anything else PAUT instrument may become more affordable and will become the favored instrument for all UT inspections.
Use of PAUT is increasing at faster rate. In my opinion it cannot completely replace Manual UT. It can replace about 60-75% in the next 5 to 10 years. Still manual UT has its advantages over PAUT. It can gradually replace RT.
Phased-array UT (PAUT) is not likely to replace "conventional UT" (UT). It may nudge out UT in more applications as equipment becomes commonly available, but as Elmar noted, there will always be places where UT can provide a more cost-effective option.