I think you might find your going to have a heavy number of users who want you to add the sampling side on, i cant think of a single person i know who would expect the synclavier to NOT have some kind of sample manipulation on it, for example the fairlight did FM synthesis, but you would hardly think of the fairlight as an FM synth, you would think sampler first.
If you made the plugin for a Fairlight and took away the sampling feature, you would get laughed out of here.
I personally think it should be a paid upgrade at worst, but one you should definitely implement in order to make it an authentic synclavier emulation, its something producers young and old out there have lusted after for as long as i can remember.