I found myself writing a lot in response to this question, so it gets its own post. The question is:
Will there ever be MAPI support in ANY of the Mac:office suite, EVER?
I'm going to answer a different question, which is, 'will Entourage ever have full Exchange compatibility?' Our goal is to consistently improve our Exchange support for our corporate users. Remember, here in MacBU, we're both Entourage and Exchange users as well, so we sharply feel the Exchange-related pain. We know we have feature gaps. Personally, I only use Entourage , so I feel every one of those feature gaps frequently.
We've made a lot of improvements in our Exchange support since the original launch of Entourage. The latest improvements that you can see are in Office 2004 SP2. That service pack brought better GAL support, improved delegation, password expiration (one of my favourite features, since I don't login to my Windows box often enough to know when my domain password is about to expire), and performance improvements. We've already announced that OOF support is finally coming to Entourage 2008.
What happens from here? Closing the feature gap is important to us. It'll make our customers happier with us, and it'll improve the productivity of MacBU in an app that we all use all day, every day. We're looking at our feature gaps and prioritising them. Which additions will have the biggest impact on our users? As we consider these questions, we're working with the Exchange team to ensure that we're on the same page as they are, and are considering the future plans for Exchange in our support so that the code that we write today is code that will continue to work with future versions of Exchange.
The reason that I didn't answer your question about MAPI is because you probably don't actually care which protocol we use to talk to the server. You care about having access to the features found in Exchange, regardless of what protocol is used to access those features.
 Well, I suppose that's not entirely true. I use OWA to check my email if I'm at home and didn't bring my laptop home.