You should never expect mods (which modify core files) to work with the next version. You are making changes to core files, and the developers don't have to respect those changes.

I make changes myself, but I always keep track of all changes in a repository, and modify any patches before applying them. It's time-consuming, but it works. I've noticed most people mindlessly apply mods, and that never ends well. I have no sympathy for them.

That said, Andrew states the following in his post:

"Dolphin see more 8 will bring a better support for 3rd party modules, templates and languages. There're some very exciting changes being made, but still, in most cases those extensions would require only minor adaptation to be operational in Dolphin 8. Some will just work."

He's probably referring to modules, which should be the encouraged method of extending Dolphin. I expect some mods to continue working, but most will probably need an update from the developer (and the same with some modules). v8 is based on v7, but there's still a lot of changes being made.

You don't need to rush ahead with v8. Andrew has said that v7 will continue to be supported as long as needed.

The release date? The tracker shows the milestone's deadline as 11/11/11, but that's for development purposes. Andrew has stated that they have release dates, but they aren't announced publicly. I can only recommend you follow the latest changes.