Well, for one, the Yugen Gaisha will disappear. All existing YKs will become a special form of KK. No new YKs will be allowed.
A new form of LLC called Godo Kaisha will be created. These will be modeled after American LLCs, but it is not yet clear what their tax status will be. Basically the big question mark is will it be possible to use them a flow-through entities for tax purposes as can be done with an American LLC. LLPs will also be allowed.
Overall the changes look good. If the new GK can be used as a flow-through entity I will be extremely happy.

I was going to form a YK this year, but I think I will wait and form a GK next year instead. A few months more won't really affect what I have planned, although I am itching to get things underway.
If anyone has more information about what is happening with this I'd love to hear about it...