This update fixes a bug that could cause the game to crash after an instance was destroyed. Additionally, some small changes have been made to make YYC compilation work. The YYC still isn't supported -- so your mileage may vary, but at the very least you might be able to get your game to run under the YYC if you're feeling adventurous.
The rewrite will fully support the YYC and GM:Studio 2.
I'm not planning on supporting the current version of the extension on YYC, but I know of one case where a game is more or less running under the YYC after this update. So you might want to give it a try and just see if you can get it working.