Since Ractive is solely concerned with rendering UI (like React), it doesn't have any opinions about where its data comes from and goes to. In theory this makes it ultra-flexible (want to use WebSockets? Fine. Want to use the Backbone adaptor? Also fine) but in practice we could probably do a much better job of coming up with some decent patterns and creating tutorials out of them, since this is a question that comes up often.
It's totally possible to just use jQuery (or AJAX lib of your choice), and do this sort of thing:
var updating;
getJSON(endpoint + '/' + id + '.json').then(function (data) {
if (updating) return; // prevent infinite loops!