>EMWA wont be accepted by ISO 15189 assessorsNo, I wouldn't imagine that it would.
Though, in and of itself, EWMA is not really a QC metric. All EWMA really does is reduce the scatter of data passed through the equation, to a degree specified by the weight used. It is still up to the technician to determine out-of-control limits for the resulting EWMA data, and to calculate type I / II error rates based on its use.
Back when I performed my own power function analyses of EWMA QC data, I found that whilst both error rates were incredibly low (in terms of Probability of Error Detection, and Probability of False Rejection) for systematic errors, and far out-performed even the most thorough Westgard Rules, there were two problems: EWMA detects virtually no randomness error (of course), and it can take a long time for EWMA data points to reflect the error being detected (e.g. whilst EWMA might be able to detect very small errors, it could take weeks/dozens of QC points before that error becomes apparent).
EWMA graphs might look great, and appear to tell you something about the underlying data, but it is necessary to specify exactly how action on EWMA QC data affects analytical uncertainty. Only then does it really become a QC metric; plotting EWMA alone wouldn't impress an assessor.