A week or so ago I wrote about ways to restore the fullscreen thumbnail bar in El Capitan’s Mission Control. None of the solutions was particularly good, however.
Well, developer briankendall has created a better solution in the form of ForceFullDesktopBar. This will cause the thumbnail bar to be always visible although it involves disabling El Capitan’s new SIP and injecting code into the Dock app.
I haven’t tested the app but it certainly sounds interesting. Full installation instructions are provided but, as usual, you proceed at your own risk!