No, it shouldn't.
IPv6 isn't yet supported by most of the internet.
As for browsers, you're confusing "enabled" with "support". They *can* visit IPv6 sites, so long as your underlying transport layers can too. But since 98% of the world's ISPs still have no support for IPv6 addressing, this "support" doesn't really matter. And since the vast majority of users on IPv6 are using 6to4- I bet you are too- the support is really not "seamless". mIRC can also understand IPv6 addresses now, just like browsers, but unless you have the underlying transport layer in place, it won't matter. Most users don't have an IPv6 layer that is connected to the internet. Making it default would make mIRC break
by default for all those users. That doesn't sound seamless to me.
Again, 6to4 contradicts your position on this issue, since it in itself is not "enabled by default" and is not nearly seamless. Users have to care about IPv6 to use it, and yet it didn't stop you, did it?
Maybe your ISP is special, or maybe you're from the future, but IPv6 is not even close to being "here" yet. The message mIRC displays is accurate and goes away after you've read it. Read it and accept what it says, and then move on. If your ISP does not support IPv6 and you have not *manually* installed a 6to4 tunnel (or have *manually* enabled Teredo), IPv6 will not work. There is no disputing this.
Until IPv6 is standard in the world's internet stack, there's no reason to make this default. The advantages mIRC gains from supporting IPv6 now is that
when IPv6 matters (it really doesn't, yet), mIRC will still work. Khaled learned from his mistakes in waiting on Unicode support. But that time has not yet come, so calm down, the sky isn't falling.
As a sidenote: you don't need to "enable" anything to use IPv6. You simply need to use /server -6 hostname to connect to an IPv6 host or bind to your IPv6 adapter. In the latter case you don't need -6 at all. This would be exactly as seamless as any browser support, and it can't really get any simpler than that.
I leave you with this simple contradiction:
If it has to be enabled explicitly, then no one will enable it.
You did.
