Could you not include an option to also manage the master list? That way, on a pre-defined schedule, the master list could be checked for live/dead proxies and remove dead proxies accordingly. It sounds simple to say but not sure how complicated the programming would be for this. Is it possible Jimb...
When checking the proxies against the given websites, the result is combined into 1 column in the proxies window. You cant tell which has passed and which has failed. I always keep this set to Google only, since Google is the important one for scraping etc. So if a proxy passes Google test but fails...
To be completely No Hands, then an integral proxy source scraper would be handy that uses advanced google search operators / footprints to scrape for proxy list urls and text files.