There's an extension called Classic Theme Restorer that aims to do it, as well as customize australis.
Oh? And what is that? "Customization is great and you should have the option to do so"? Try having a "classic theme restorer" with Chromium.
> it may get broken again in later versions
Future changes may cause incompatibilities in any project. That is why such changes are released in major new versions so that add-on developers have plenty of time to make adjustments and fixes.
It is supposed to get Chrome extension support this year too, and if I ever had the time I'd try to expand their sync options (currently Opera + Chrome) to sync tabs and such.