Which version of episerver are you running? Will have to ask the devteam about that but I believe that tinymce in the latest episerver release is not that old :) they are using 3.5..something and tiny is in 4..something. So hopefully they will update it soon. If I were you a quick answer from episerver would actually be to just use twitter about this issue.
May not be that old in the newer versions of EPi but most of the plugins that we would like to use require tinymce 4.x+
I've just checked in EpiServer 11 Alloy Tech project and TinyMCE is still version 3.5.11 as it was in EpiServer 10.
...same version as was in Episerver 10, 9, 8, 7, 6, 5 (possible even earlier, can't recall). Yes, we're still using the same old editor since 7 years. Good news is that an update finally seems to be in the works, see https://world.episerver.com/forum/developer-forum/Feature-requests/Thread-Container/2017/3/tinymce-version-4/
Was wondering if there are any plans to upgrade tiny mce in the near future? It would be of great benefit as a lot of custom plugins require a newer version that what epi ships with.