Backwards compatibility is very important and esp. for almost finished projects that can't switch to the new toys because of time constraints or other reasons. 3DGS has always been BC for a certain period of time (before removing it) when switching languages (WDL vs. C-script and now C-script vs. Lite-C). It would only make sense to do the same for physics. Your old ODE code will work just like it did before and if you want to upgrade to whatever is chosen then you can and the engine will use the new one.