As far as I know, you'd have to write a program to constantly monitor your folder to delete files if it got over a size. I think your software could just delete the folder and stop syncing if things get out of hand. This would induce website authors to keep their sites small, otherwise they won't sync. So, if you wrote an HTTP server that managed and constantly monitored your sites/folders for you, got a system-wide list of BTSync websites, and had your HTTP Server serve up the pages for you, yes. This looks like what "SyncNet" does, so it just needs to add a max size feature if it doesn't have it already. Of course you'd have to add the search engine. The BTSync config file may have an option you can specify to limit size though.