If it were to succeed with one platform, it would have to be servers. People don't spend money on servers to go and install games/photoshop/office on them- they install apache, sendmail (or whatever they choose), and go on their way- that is, if they install anything at all. Usually they get the server with all the software they need, throw in the pertinent info like their DNS names, and let them chug. With an X86 server, Apple wouldn't need to implement special features like QE, rendevous, or any other enhancements simply because they're not needed. That's the very reason why true server admins hate Windows- there is too much extra crap running for an effective/secure server. With Unix/Linux a quick ps command will tell you what is running, and almost every service can be shutdown and restarted independantly. Sounds a little bit like OS X, doesn't it?
The only problem with this idea is that I don't think it would be successful in the long run. Serious servers don't even run GUIs, they're all CLI based for easy remote adminstration. OS X would be extraneous for them because they would never use the Crown Jewel of it- the GUI. Most of the time these servers don't even have monitors or keyboards hooked up- everything is done ssh. Small, workgroup servers would be the ideal target for these- usually they run Windows or a Windowed Linux system. As long as they didn't have any kind of proprietary software, then a Marklar product may work for them, but then you face the uphill battle of "Why switch?" The benefits of X wouldn't be realized in this scenario because, once again, a server is a box that just sits there. Anything can do its job. Thus, there'd be little reason to spend the time (no matter how little it would be) converting admins to the new box.
It's a nice idea, but the market for it is so small that it wouldn't be worth releasing it. So, I don't think it'll happen.