Engines VS rails3

So in the recent doubleshot http://afreshcup.com/2009/04/24/double-shot-438/
there is the comment "Tips for writing your own Rails engine .... I’d
wait for Rails 3 if I could myself."

What is planned for Rails3 that is preferable over Engines? Would not
moving to Engines now make it easier to adapt to Rails3 anyway?

I think the idea is that Rails 3 will be more modular and have more
stable APIs for plugging in engine-like functionality. The engines
support in Rails 2.3 (at the moment, at least) is really just the
simplest possible to support an app directory and loading routes.