Once again, with apologies to John Gruber…
Q: Do standards-based developers have to use
X-UA-Compatible if they care about progressive enhancement for future browsers?
A: As I see it, yes.
Q: Doesn’t Internet Explorer already offer a fine-grained way to target specific versions?
A: Yes, definitely.
Q: So if there was a problem with the IE6 to IE7 transition, doesn’t that mean people weren’t properly using an existing tool which could have future-proofed their sites?
A: You may rely on it.
Q: Given that, is it likely that people will properly use a new tool that could future-proof their sites?
A: Very doubtful.
Q: Chris Wilson says that HTML 5 documents won’t need to use
X-UA-Compatible. Since IE8 will be Microsoft’s first implementation of an unfinished specification, isn’t it likely that there will be bugs and that designers and developers will need to rely on them to get the intended rendering?
A: Most likely.
Q: So when IE9 is released, won’t Microsoft be back in the same situation of “breaking the Web”?
A: Signs point to yes.
Q: What will we be asked to do when IE9 comes out, then?
A: Cannot predict now.
Q: But if it goes down this course, IE will need to keep adding new version-targeting mechanisms with every release?
A: It is certain.
X-UA-Compatible won’t really solve the problem of forward compatibility for IE?
A: Outlook not so good.
Q: Has anybody actually sat down and thought this through logically?
A: Don’t count on it.
Q: Why are so many big names in the standards world so non-chalant about it, or even supporting it, then?
A: Ask again later.