I'll be looking it over in the bookstore first before I decide on getting it - mostly due to the mechanics aspect. Consider, for instance, if the weapon is lost beyond any ability to regain. Suppose it is destroyed in some manner.
Now, for most of the mechanics, this is a minor thing. You regain the decreased hp, saves, bab, etc. But some of the weapons decrease the skill points you earn upon gaining a new level. That is a penalty that forever marrs the character even if the weapon is lost and never regained. Also, what if - by chance or poor DM design - a player ends up with two weapons of legacy. So far every single one has penalized bab, saves, and hp. Do these stack? Also, does the penalty to bab apply when using the weapon (in which its increasing +1 enhancements are nothing except damage boosts - as the weapon is never more than a +1 attack due to bab decrease) or do these penalties only apply when using other weapons?
There are just too many potentially problematic aspects to the mechanics - as they seem to be - to justify using them, at least as they current seem to work. Once the book comes out hopefully most of the questions will be answered in a way that shows all these fears were for naught.