The new Eclipse Mars comes with some notable improvements, particularly the new installer. I figured I would always be dealing with Eclipse through a zip archive, but it looks like they are finally trying to make things a little easier for us.
So, there was a little change in the beloved Remote System Explorer plugin as well. As this FAQ explains, it looks like RSE is now a separate project from TM, or Target Management. As a result, when you install the RSE plugin in your new Eclipse Mars installation, you will notice that the Launch Terminal command is no longer present. I suddenly realized this to my great consternation, and I was lucky to find a a bug report for this sparingly discussed issue.
As you will notice from my comment, my continued scouring of the Internet finally led me to a YouTube video with a comment that addressed this very issue. It turns out that you now have to install at least two separate plugins, TM Terminal and TM Terminal View Remote Systems Explorer add-in, which are found in the regular Install New Software window. After installing them and restarting, if you right click an RSE connection, you will see the Open Terminal… command which will let you use the familiar RSE SSH terminal. From what I understand, they’ve set things up now so that such a terminal capability is now more amenable to extension/customization. I’m simply glad that this feature is still available, even if some labor is required to get it back. I do not see any mention of needing to install the separate plugin when I peruse the Target Management site and FAQ. I hope this article is of use to other Eclipse and RSE users.