I've never used emacs, but am interested in to try it for its 'org-mode'... I understand that its now possible to view images inline - but can GIFS be viewed inline?
And then, is it possible to view video, audio, pdf, web, etc with emacs OWN viewer? If not (especially for uncommon file types), via a relevant application of choice (excel, chrome, etc) that opens in a separate PANE, but same window?
If so - are these hard to implement?
First, in Emacs, what the rest of the world calls 'windows' are called 'frames', and what you refer to as 'panes' are called 'windows'.
You can open images, pdfs, and webpages in an Emacs window (pane). Open images as you would any other file, and any recognized format is displayed as you would expect. Emacs has its own viewer for PDFs, and if you are on Linux, an even better one is available called pdf-tools. Emacs has a built-in web browser, although it displays pages in a pretty basic way relative to Firefox or Chrome.
You cannot open Excel, Chrome, or other GUI apps in an Emacs window, but you can launch them (or any other program) from Emacs, and have it run in its own frame. When opening links to external files from org-mode, Emacs will try to find an appropriate program. So if you have a link to an Excel file in your org file, the command org-open-at-point will open that file in Excel. (you may require some configuration depending on the file type and how your operating system is set up. The details are in the org-mode manual).
