Even in v8.1, the short answer is no; you cannot positional-statically display the content of a variable without a plugin ... OR additional vim scripting.
However, Decho plugin does allow you to write info into another screen/buffer in a live manner using function calls.
And DBGp is a debugger GUI for Vim debugging session (written in Python and Vimscript) also will write variable values to another "window" pane (or grid box) in a static cursor positional manner.
Both of which you could extract certain Vim script codings that deals with placing variable values in another actively-displayed buffer, in which you could put these snippet of codes into your local
~/.vimrc and that would be the solution for your 'plugin-less' approach.
Decho (by Dr.Chip) or
- or this updated Vim debugger (DBGp) plugin in Github.