Completely strip any hidden formatting when pasting into TinyMCE

I’m not quite understand what you need but I think that you trying to insert text as plain text from anywhere: Browser, M$ Word, Pages.

For this purpose you can use Advanced TinyMCE Configuration plugin. After download and activating this plugin requires manual configuration. This solution better than code you suggested in question section above).

Option name                  Value
paste_strip_class_attributes all
paste_remove_spans           true
paste_remove_styles          true
paste_as_text                true
paste_text_sticky            true
block_formats                Paragraph=p;Header 2=h2;...

All of these parts (parameters) of config may be founded on Tiny MCE documentation pages.

1. paste_strip_class_attributes — old attribute from 3.?.? version
   for removing all tags attributes like href, alt, class,
   onError,..
2. paste_remove_spans — also from 3.?.? version. Enables you to
   remove all span (inline?) elements while pasting.
3. paste_remove_styles — If true, removes all style information when
   pasting, regardless of browser type. Pasting from Word 2000 will
   cause tinyMCE to error.
4. paste_as_text — This option enables you to set the default state
   of the “paste as text” edit menu option. It’s disabled by default
   but can be forced on by default.
5. paste_text_sticky — Keeps Paste Text feature active until user
   deselects the Paste as Text button.
6. block_formats — additional configuration for my site 🙂

This config working fine on my sites and I always insert text in TinyMCE like a plain text.

Also helpfull plugin for TinyMCE tuning TinyMCE Advanced.