The REST Service opens great possibilities to the XPages. But what, if the users want to use the XPages application offline and locally? In that case the REST Services can't be used for the XPages development at the moment.
Please make the REST Service available to the Lotus Notes Client too. If shouldn't be a complex task, because below the Notes Client the Expeditor is running with a web-container, as it is in the Domino 8.5.3 now. As far as I have understood, the REST Service is an OSGI servlet that is running in that web-container.