Commendable I must say.
We obviously don't know what aspects are 'engine' and what are 'core' (as it was always called core3 as a whole to us before now). So is the core going to be everything haven't sorted out and the engine everything you've already done? Or is it more modularly explainable than that?
Is there a promise of it staying SVN or will it be closed from there when you have what you want?
I'll say again, I think this is a great step forward and wish all teams would make all their code public, though I know that won't happen
Good luck with this guys.