I like most of your ideas a lot.

Glissando/Portamento would be really cool, same with envelope follower and tremolo and other effects.

-How about arpeggiating frozen chords?

-A freeze that triggers a synth. Maybe string ensembles, mellotron, analog pads or choir/voice synthesis.

-Vowel/formant filters could be nice, especially if they can have movement related to the input signal.

-Would it be possible to use SIFT technology to track the input signal and use the pitch information (in addition to amplitude) as a control  signal to manipulate the freezed part? Pitch dependent auto freeze? Pitch dependent resonator? Pitch dependent ducking?