Maybe in a future update, you would consider implementing a "Clouds" like freeze function with a reverb that can be played after the freeze via midi.
I just looked that up, interesting module. The closest thing I have made to a spectral freeze function is actually in Virta. Although it doesn't have a freeze feature now, I could add one pretty easily.
Kaivo would be a bit harder because there is nothing like a spectral processor in it. The resonators and body are all physics-based and it's hard to imagine how to freeze them in a useful way.
Take a look at Ableton Live's freeze function in their reverb module. Just as a test, maybe you could add a freeze button in the Aalto reverb section, an input to control the freeze pitch, and an output into the envelope section. Once the freeze button is enabled, you can repatch by removing the pitch to the oscillator, into the reverb section to control the pitch and envelope of the freeze. I am just trying to think about things you could feasibly do that would not cause you too much time investment re programming things in your plugins. I figure this feature if too much of a pain to do, may be better suited for Aalto 2
Implementing a freeze button into Virta would be pretty neat (not going to lie).
Much more likely to happen in Virta! I want Aalto's reverb to be a super-simple, one-knob device in the spirit of the Arp 2600.