Hi Steve,
If I were not sensitive about my tender years, I would admit to watching 'rag rugs' being made
I have cleaned two or three of these, many years ago, and they can present several problems.
Firstly they cannot safely be pre-vac'ed with an upright cleaner, so beating (from the back) is the first stage, followed by air-only vacing from both sides.
Secondly, several different dyes could have been used, so pre-testing must incude each - I would sugest all test areas be covered with terry towels, topped with a pressure board and left for at least 20 mins. Alum, if you can locate some, can be a useful stabiliser for some home-brew dyes.
One of the rugs I cleaned was somewhat fragile in that I felt that some if the rag pieces may be drawn into the extraction tool and be pulled out as the tool advanced. (This was more likely due to the fact that felt-like materials were used). It was also extremely dirty. The solution to this was to treat it as an antique tapestry and clean through a muslin nappy held firmly in place.
Another option is not to machine extract but, haveing treated the rug with the chosen cleaning agent, to construct a press composed of seveal layers of terry towels, then the rug, then several more layers of towel, topped by a weighted presure-board. The whole sandwich is left for 6-8 hours, with the inner layers being changed after 30 mins., then at hourly intervals.
Clearly this latter method is not suitable for on-site cleaning but if you take the rugs home they would take up little time each evening untill done.
Subject to pre-testing, one of the micro-splitters, at high dilution (1:20) may well be suitable.
I do not need to comment on pre-qualification to a man of your experience, so I close with a wish of good luck.
John.