Maybe we editors should include a REALLYIMPORTANT flag too. But the fact that I never thought about it before reading that article suggests it's not really important.
If I do have something REALLYIMPORTANT (which is exceptionally rare), I plaster it all over so that it's practically not missable (esp. in code review). Sure, highlighting _that_ comment might help a bit during development, but I really don't think that use case is worth highlighting _all_ code in that case. But it could be a 'nice-to-have' for syntax highlighters.
That little bit of extra information, which only takes a few seconds to type, can save a lot of people a lot of time afterwards.
I do this, and add any addition "why" or other needed detail indented under the first summary commented line.
Making the comment large is good enough for that. But a really different tag may help here.