this maybe or maybe not be along the lines of what your saying, but the new sound forge 7 offers plugin automation, so that way you can automate/morph from one effect setting to another over time.

or even with cubase's automation just take a had full of controles and change them over time.

but as for a gradual swiitch between piano 001 and patch 002 on a synth. i don't think they have that as a standard on all synth/effects right now.