Microsoft is rebuilding its Edge browser on Chrome and bringing it to the Mac

Does it though? Chromium or rather the Blink engine is very different from IE6: It's in active development, it's available for multiple platforms, it's open source and it follows web standards as they developed.

The old days of IE6 were very different in that the web standards were stuck in a limbo (remember XHTML?), IE6 had features that were specific to Windows and could not be ported to other OSes without bringing half of Windows with it (ActiveX) and IE6 was full of quirks and bugs that directly contradicted the standards.

If you made a site to work correctly in IE and using all of its features it was very unlikely that it could work unaltered on any other platform and, again, IE itself was inherently non-portable.

Conversely, if you made a site targeting standards, you would a) lose out on features the market wanted and other sites provided (back then, even AJAX was an IE-only feature for a while) and b) the site would not work at all on the browser with 90% market share.

Today the standards move fast enough and are implemented quickly enough by browser vendors that your standards-compliant site will not be at a competitive disadvantage. And even if Google decided to stop being standards compliant and removing features they don't like or adding features we don't like, Chromium is open source and Microsoft is powerful enough to keep the eventual fork alive.

As somebody who lived through the bad old IE6 days, I see this current situation as a much more positive thing than what the IE-of-old situation ever was.

To the contrary: The way how the siutation looks like right now, we are finally at the position where every OS with any significant market share will now come with a default browser that supports the majority of the current web standards and that will be updated often enough to stay up do date with the standards as they evolve.

While Edge was much better than IE in that regard, have a look at caniuse.com and compare what's offered to-date by the default browser shipping with Windows to what's offered by any other OSes default browser.

Edge was still based on Trident, no matter what MS was saying. The decades of technical dept remained and by being tied to the OS, Edge could only ever be updated every 6 months anyways.