We used to 'clean' a group of very high end clothes shops that had this installed in all their sites, it does look fantastic when newly fitted but it is virtually non-cleanable and very quickly soils especially with high footfall.
I classified it as very high maintenance with limited results at high cleaning cost and got into trouble with the manufacturers and suppliers as a result
Some of you might remember that in the roll they used to have slip of paper that recommended cleaning with white vinegar, it was complete nonsense of course but it allowed them to able to state that it was cleanable, I think now they recommend the HOST system which goes right back to what we used to say in that it is very limited in its results and will not remove the vast majority of stains.
I remember one particular famous large restaurant on the Kings Road that had a major refit and had Sisal fitted through out , we were asked to go in and 'stain protect' it. It looked fantastic but I knew spraying down some old slop was not going to do a thing to protect it and told them so. Within a month we were back while still looking okay had lots of red wine, coffee ,tea, etc stains on it along with loads of cigarette burns.I told them what to expect and what I had said previously, we cleaned with no real difference other than removing top soiling they were very disappointed of course and within 6 months the carpet was up and replaced with wood flooring.
The problem is Sisal when soiled and stained will pull down the appearance of any place that it is installed and so any kind of maintenance goes out the window because very quickly they know there is no point in trying to keep it clean.
Who ever does come up with a system of effective cleaning will make a fortune by the way and could get exclusivity as a result,I think just about every body has tried and given up.