Read
Windows Live Messenger 9.0, it's discussed over there.
In short: Beta1 wasn't going to be updated for a long while and it happened to be fairly easy to update Plus! to make it work on beta1.
The new leak (beta2) is different... new builds are expected within a few weeks. If you read
LiveSide you'll see they already have news about unreleased new features. So a lot will still change in a short period of time. It would be a waste of time to try and make Plus! compatible with this build when a new (completely different) build releases maybe a week later.
Also, there are a lot more internal changes in beta2 than there were in beta1, making Plus! compatible wont be a quick fix like last time.
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