Hi Steve,
Most fabrics can be cleaned using water or foam, there are the odd exceptions of course, but less now than there used to be a few years ago, with the demise of glazed cottons & viscose velours. I use only HWE combined with hand cleaning. Anything I can't do with that I walk away from. Maybe two jobs a year.
I used to have a small 'Extractor' spirit m/c which I very recently sold because I hadn't used it in about 4 years.
I gave up dry-cleaning curtains years ago as I found that I made very little money from it, even allowing for re-cycling the solvent.
I found that thorough vacuuming followed by hand cleaning with a damp sponge & upholstery cleaner or one-step produced just as good a job far quicker and at negligible cost. Much more profitable.
The main problem with having a dry-cleaning facility built in to your normal m/c , is that the sludge tank needs to be scrupulously clean so that you can re-cycle the solvent. This means scrubbing the tank out the night before, and doing dry-cleaning as the first job of the day before cleaning any thing else.
Bryan