I'm not going to be Jim Keeler and be aggressive about this, but even though it would probably never be efficient, let alone work, what if there was a bagless Kirby conversion that used Rainbow esque water filtration. It would likely be bulky and inefficient, but it seems more original than a Eureka Optima bin with some PCV pipe for $100.
~This was just a random thought I had thinking about the Kirby Shampoo system
~This was just a random thought I had thinking about the Kirby Shampoo system