I strongly believe it should be part of the core.
In matter of fact, when I was working on it, still on CakeDC, I already developed it thinking in one day bundle it with the core. That's why its so dependent on the CakeSchema, for example.
The decision is not mine, but for me is a +1
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Renan Gonçalves aka renan.saddam
Software Engineer at TrueServer B.V.
CakePHP Core Developer
Website: renangoncalves dot com
Amsterdam, The Netherlands