At the moment it is only possible to expose microflow as a webservice operation (Bottom-Up approach). Sometime we have been requested to expose webservices as per client WSDL, which is currently impossible in Mendix. To overcome from this issue we are having a workaround, as exposing an intermediate webservice in front of Mendix as a middleware and this middleware application consuming webservice exposed by Mendix.
I would request a feature to expose webservices by top-down approach in Mendix.