Remember that Realm Works Cloud Service is
already supposed to be a paid subscription, and player access (including via the web) requires Cloud Service. The only stated reason that they're not currently charging anyone for Cloud Service is the long delayed launch of the Content Market.
RW FAQ: My GM does not have Cloud Service. Can I still use Player Edition in his/her game?
RW Cloud FAQ: If I have cloud service, will my players be able to view my realm for free through the web app? (Emphasis mine.)
Plans may change, of course.