XBMC and Plex are very different solutions. The largest difference in relation to channels, is that Plex channels run on the Plex Media Server and are intended to serve content to a wide variety of apps across multiple platforms, possibly concurrently. XBMC, though, is designed as a single program intended to run on a single system at a time. That means that some solutions which work for XBMC plugins, such as opening a separate browser window to view content, are not practical or functional for Plex channels. It is also worth noting that the Plex Channel Framework is very different than what XBMC uses for its plugins.
Note: Users often request that a particular XBMC plugin be "ported" to Plex. Due to the significant differences in how plugins/channels work between the two applications, there is simply no easy straightforward way to "port" an XBMC plugin to Plex. In these cases making a Plex channel is a completely new project may not even be possible at all, depending on how the source website makes content available.