> I fear that this topic would drift off into some large scale discussion in a public board (especially with people like Asmageddon around).

I don't. Actually I am quite positively surprised of how few discussions really drift off in our forums. And if it does then we can still lock or move branches. I'd volunteer to do that if that makes you change your mind.

> I think it is better to limit the number of opinions to those of the developers here because we will do the actual maintenance work for creating updates and patches.

With the same argument you could also move most development discussions into the private board.

Another option would be to make it publicily readable but let only developers reply to the topic. But I'd still prefer the all-open variant.