this is really a question for jps. Is it OK to include the GPL-licensed "ddeclient" command-line utility (from Emacs)? IT provides a simple way to send DDE commands to programs that implement the DDE server protocol (including Acrobat, Sumatra PDF, etc.).
DDE functionality is provided by the pywin32 package, but that's a pretty big dependency for a single package!
Alternatively, one could use ctypes to access the ddeml DLL functions directly [or perhaps ST might implement DDE calls in a future version...]. This is the hard way so it would be nice if one could take a shortcut!
PS: the LaTeX plugin I am developing is shaping up nicely, IMHO. I'd be honored if you wanted to include it in a future release.