I keep dreaming of making a real-time phrase trainer!!!!
Housed in a rocker (wah-type) pedal, full down would be normal (bypass) but as you played through it and tilted the rocker bit, it would graduaalllyyyy sssssllllllllllllooooooooowwwwwwwwww ddoooooooooooowwwwwwwnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn...... Until it froze, looping forever! And you walk off stage leaving it locked in a frozen moment of time...
Hard to build, completely amazing, fairly useless in a band situation, and hard to build. It would be beautiful, and hard to build.
And with a 'lo-fi' option switch!