All these extras sound interesting but escpecially for #1, #2, #3 and maybe for #5 I fear incompatibilities to other tab related extensions like Tabmix Plus.
But I'd like to suggest another feature that I wished for a long time since I started using Colorful Tabs:
• Generate colors from the site's favicon
I used ChromaTabs Plus (https://addons.mozilla.org/de/firefox/addon/chromatabs-plus/) years ago before I switched to Colorful Tabs.
I like Colorful Tabs a lot more but I really miss that special feature. Maybe you could use some of that code if you decide to implement this.