navindra
Fist off, @SychO is working on a tool that will automatically apply some of the most occurring changes for extensions from 1.x to 2.x. This will help extension maintainers to upgrade extensions faster. Testing the extension and taking care of the remaining changes for this upgrade is still going to be manual labor.
Secondly, we've had a similar situation moving from beta to 1.x. Back then we did a fundraiser to guarantee some of our most used extensions were patched by the @FriendsOfFlarum. We will do something similar for 2.x.
And yes, we will lose a lot of extensions due to incompatibility, but 2.x brings a lot of improvements that will make building extensions easier and allow more advanced extensions to happen.