For some time now I have been considering ending development of JCE MediaBox. It is quite a popular extension, and has existed in one form or another for Joomla 1.5, 2.5 and 3 since at least 2008, initially as JCE Utilities, then later as JCE MediaBox.
Despite this, it's development and maintenance are obviously time consuming, and take away from time that could be spent on the JCE Editor. Unlike JCE Editor, there are a few (perhaps better) alternatives, Yootheme WidgetKit and RocketTheme RokBox to name two, both free, actively developed, and supported by JCE Editor through add-ons.
A difficult decision awaits. Your comments, via twitter, would be welcome.