I’m not planning to do this now but I wanted us to decide if that’s something we want to do.
IMO the rss macro is not a core macro (there are actually not a lot of needs for it) and should be moved out of platform. This goes in the direction of our quest to reduce the size of XS.
Moving to contrib also means that it won’t be supported anymore by the XWiki dev team. But if it’s not used in platform then we probably didn’t support / maintain it very well so I guess it’s fine to move it, so +1.