Actually I have not given you an exact time frame because the migration of the older forward mapping projects is something that is not completely defined on our side, I must admit. We will definitely provide a way for the customers to move their projects to the Visual Designer approach but, doing an automatic upgrade is a risky approach due to the fact that clients writing forward mapping are usually writing their own logic in their persistent classes and there is a possibility for this logic to be gone after we uprade the project and generate the classes ourselves. We are thinking about a feature of the designer that would allow you to include your won classes in the designer without us touching those classes and not generating any code for them so that your code would stay the same as it was before. However that is a feature we have not yet developed and I believe that the only real time frame is Q1 2011 release.
I really apologize for the inconveniences this might be causing you, but this is a really delicate step and we thrive towards doing it in the safest way for our clients.
Also, in the meantime, maybe you could have a look into the fluent mapping API which is another way for you to map your classes using custom code. However if, you are a fan of the designer and would like to do more drag&drop, this is not the approach you should go for.
All the best,
the Telerik team