"bring what Google naturally calls "legacy application support – which includes Microsoft Office desktop apps – to Chromebooks."
Legacy is a misleading name obviously. Not only will it outlive whatever crud ChromeOS applications are but ChromeOS itself can only be built in such a "legacy" environment. Does this make ChromeOS a legacy OS?
The term modern and legacy in computing is being misused. Modern generally means "short lived gimmick" and legacy means "boring and difficult to monetize".