Switzerland already does this, I think.
Sort of, the co-pay/excess is capped as a function of your income, but insurance is still very expensive. Someone on a low income will very likely pay well over 10% of their income on healthcare if they have any sort of health problem.
Based on the Swiss experience, I don't think capping healthcare would be a solution, as the cost of healthcare in Switzerland is still well above what it is elsewhere in Europe, and is possibly the major political issue at the moment.
