I think I know where you're coming from, and there's a lot to say for both early releases, and not doing so.
I've also seen emus in the past, that had been developed in silence, and then suddenly *BAM* there was an emu emulating system X very playable, and everyone was amazed.
The other way is the slowly progressing emu, step by step WIP showing every little detail.
It's up to the developers, and I think both methods will generate quite a bit of hype. The sudden release of a working emu will cause a similar hype explosion, pcsx2 also gets the hype going, but not as explosive as, say, when chankast or ultrahle got its first release.
On the other hand, people might get their hopes up, and be dissapointed with pcsx2, if theyre just in there for playing the games; on the other hand, it great to be able to follow progress for those interested.
A "danger" for pcsx2 would be a different emu suddenly appearing on the scene doing what chankast did; that'd definately put pcsx2 out of the picture. It's likely to happen too, as it happened before. I just hope everyone realizes that too.