The roads I take...

Since our rework of the SeaMonkey suite to using the "new toolkit" on trunk is making good progress, the SeaMonkey Council has talked about setting up criteria our trunk builds have to meet so we can release a first Alpha for SeaMonkey 2.

The relatively small and compact list of those criteria is:

1. AUS (automated update service) needs to work,
2. L10n builds need to be usable,
3. no major broken functionality,
4. profiles created or migrated with Alpha need to be in a state that doesn't need re-migration until final.

We agreed that not having two preference windows (like we do have in current nightlies due to the ongoing transition to the new one) is along the lines of c) here, and b) needs password and download manager work, maybe even some shell service stuff.

Being feature-complete or doing any kind of feature or locale freeze is something for the Beta phase, rather than for Alpha.

Point a) in this list mainly means that users of Alphas should be able to utilize AUS for upgrading to later builds, esp. Beta and final builds.

The main requirement for d) is that users who migrated a profile with Alpha don't need further "manual" migration to keep using this profile (or even throw away and re-migrate it) with later builds in the 2.0 series, including final and minor updates.
Things like changing to places history should automigrate existing data, so there's no problem with doing that post-Alpha, a small question may remain open for how to deal with people migrating from Thunderbird and having feeds in those profiles, as we probably want to have them pick those up once we support them, but they may look strange in mailnews currently.

The SeaMonkey Council will start marking Alpha blockers according to that criteria in the next days. Note that minor annoyances probably will not block an Alpha release, though we'd like to see them fixed. We're not targeting a fully cleaned up final release yet, this is still an Alpha and it's neither supposed to be feature-complete nor regression-free, but ready to be tested by a significantly wider range of community members than our usual trunk nightlies.