I'm going to argue out of ignorance. I am not nearly as close to the Nuxeo guys as I am to many other Zope people, and I don't have very much direct experience with CPS at all. However, I want to speculate a bit about the recent announcement that Nuxeo 5 (which is basically the evolution from CPS 4) will be 100% J2EE, in light of some realities that are abundantly clear at my existing employer.
CPS always felt a bit reclusive in the Zope world. Florent, Leonnart, Jean-Marc and Tariq (I probably spelled half of those wrong) were visible in the Zope 2, CMF and Five spheres, and I really like them and their work. However, CPS itself was (is) one of things that we often thought, "oh, it's really powerful and good" but never really used. Maybe it's because I don't speak French. Maybe it's because I'm addicted to the Plone community. But CPS was (is) Nuxeo's baby and business model. Which is perfectly, perfectly fine (and it's still fully open source, as will Nuxeo 5 be). Florent and Leonnart in particular contributed tons to CMF, Five and other parts of the stack. But it's these contributions we'll miss (presuming they stop, which I hope they don't), not the CPS-specific Zope technology that we never much re-used (or got around to looking at, perhaps).
I've been doing some J2EE work lately. There are things that are quite good about it, and there are things that are not. The Nuxeo 5 FAQ says that Java can be pleasurable with the right tool support. Maybe, but I can count on all my hands and toes the number of hours I've lost to trying to get the build system to play ball, configuring various tools and plug-ins, and debugging strange errors in non-readable code. I'm sure it'd be much better if I worked with Java day in, day out, got tons of training and had it all laid out for me by a standard build that some soul had spent months setting up and testing. At my employer, that'll never be the reality.
I have some particular beef with JSF (Java Server Faces). It may be the best Java's got for web UI, but it's still painfully slow and often unpredictable (I see some component tree state caches that don't invalidate properly, for example). It does not play well with JSP at all. Java Facelets help, and even have METAL-style macros, but don't even think of showing a complex JSF-based UI to a web designer. It's hard to know where the line between HTML and JSF components go, and JSF components still involve writing HTML to an output stream with Java code (they say they're working on it). I'm sure I just don't understand it, but I have seen supposedly cutting-edge JSF work (in Alfresco), and it's still awkard (single templates having a myriad of responsibilities).
The reason that I don't understand it because the stack is a mile high. JSF builds on JSP builds on servlets builds on streams builds on ... EJBs are just scary. Hibernate is quite good, actually, but I found it hard to debug. I'm quite quick at picking up new technologies, but the amount of technologies I have to understand to be productive is so large. I really wanted to use Spring, but that was another book to read. Again, if I did it day in day out and could affort to take a month on a training course or two, I'd probably do fine, but it's not the reality.
Will Nuxeo's programmers be happier with Java? Perhaps so, it may fit their brains well. They may find that it pays back in terms of stability, predictability and scalability (I'm somewhat sceptical of those arguments). They will certainly find it easier to hire new, talented developers.
But I can't help suspect that this has a lot to do with commercial realities. Alfresco has created a lot of noise off a product that's very, very impressive on paper and reasonably impressive on screen. It doesn't have anywhere near Plone's customisation/application-building story, for example. But if you read the spec list, it includes things like JSR170 and JSR168. Java standards (supposedly) for content storage and portlets, respectively. It talks to Lucene and Hibernate and MyFaces and MySQL, it uses Spring. These are things that are often singled out as "best-of-breed" open source components.
A digression... the Open Source in Java Enterprise world is bit of a parallel universe to the one we know in Zope and Plone. Different kinds of people hang out there. Investment comes from heavy-weights and Sun specification working groups. Apache/Jakarta are kings (and they have a lot of very, very impressive software)... end digession...
But Gartner goes out and says, "demand JSR170 to avoid lock-in". The ZODB makes IT managers quiver (call it an object store, not a database, Matt Hammilton says). Butler says, "demand JSR168 to integrate your applications with your portal server". IBM tell you, maybe it'll even work. We have viewlets and component architectures that make those things seem like last year's fashion, but that isn't what people buying IT look for. And probably for good reason. They shouldn't invest their money in unproven solutions, hard-to-integrate platforms or dying products. It's often a lot of money on the table, and being conservative is often a good thing (whether they always get what the bought is another story).
So, for Nuxeo, I'm sure that their clients will be very much more impressed if the 10 minute PowerPoint sales pitch includes a number of technologies they have heard about. It makes a lot of sense, especially since their stated target is the ECM sphere, and I'm guessing their customers have a lot of similar Java technologies already deployed. And I am really glad that there will be a credible alternative to Alfresco in the Java-based ECM/DMS market.
As far as Plone is concerned, I think our edge will always be in flexibility and agility. I can do things with Plone much faster than I can with any other platform, and I can develop cleaner, better-tested components using Zope 3 technologies than any other platform I've ever seen. At the same time, people like Enfold are doing incredible things with integration, and Plone 3.0 should put us back on the innovation curve with exciting new tools and technologies. Mostly, I'm not worried because the Plone community is so vibrant, with so many cool people and such a lot of friendship. In open source, this is worth more than technology.
But at the same time, I'm very eager to find out what Nuxeo's very talented developers will manage to come up with. Hopefully, I'll have a chance to sit down with them over a drink and get their experiences straight from the horse's mouth. Nuxeo.com/org have a commercial story to tell. I wish them the best of luck.