Hi Frank, just to clarify...
Linear and spline interpolation methods are supported in pss-hb and hb (and all subsequent small signal analyses) and envlp.
pss-shooting can be used with the nport in some circumstances. Linear and spline interpolation methods are not supported for Shooting QPSS/QPXX, Shooting autonomous PSS/PXX, and Shooting Envlp.
Things have been rapidly improving with the nport - when I have an update, I'll be sure to report it.
And I fully agree - if enhancements are desired, make sure to contact Cadence Customer Support and request an Enhancement CCR.
Staff Support AE, Global Customer Support
Cadence Design Systems, Inc.