'use some no clog dacron as a pre-filter...'
You'll have to tell me more about 'dacron' - how does it work? Why doesn't it clog? If it does work, why isn't everyone using it? How can a material filter not clog? It seems to me that either it's trapping dust particles and clogging, or it's letting them through. I'm genuinely interested to hear more about this.
With regards to the bagless conversion...even if, and that's a BIG if, there's any initial improvement in performance, it will not last. The filter they use will clog. A filter-based bagless system has a separation-efficiency of less than 50% - meaning that more than half the dust you pick up will need to be held back by the filter, rather than the cyclone system. A filter-based cyclonic machine, loaded with 125g of dust, will lose 80% of it's airflow.
Why buy a bagged cleaner, then bolt on some botched home-converter contraption!? If you want to save on bags, invest in a decent bagless machine, designed for the job!
I would guess that using this would void Kirby's warranty, too, since it's a non-gen part?