in function ezpMvcConfiguration::runCustomFilters, there is a bug that prevents any filter to be loaded:
the name of the filter interface is built like this:
ezpRestPreRoutingFiltersFilterInterface
instead of
ezpRestPreRoutingFilterInterface
So whatever interface your filter class implements, it will never satisfy requirements an be rejected

This happens because of the line 149:
$interfaceName = 'ezpRest' . $filterName . 'FilterInterface';
should be
$interfaceName = 'ezpRest' . $type . 'FilterInterface';

Easy fix isnt'it? The question is: how comes nobody found it so far?