this is a duplicate of a post already made.
However, to answer your statement. Of course they will make a zbrush 4. The companies have roadmaps for software development longer than just the next version.
Each of the two contenders have very goals which will greatly effect their development process over the next few years. These will help develope strengths for their software over time.
Zbrush can go in any direction the company wants to take it (this is a very good thing!).
It will probably be ahead in innovation and tools for at least the next several software generations. People used-to complain over the GUI, thats because Pixologic is trying something new and different, good things can happen when companies try new and different things. They offer amazing plug-ins free which enhance the artists workflow. Zbrush is production proven. Their tools are complex, people just need to get used to the different setup. Zbrush also has a great foundation in the industry. A lot of people are using it and loving it. My guess is pixologic has some amazingly informative and helpful insight from industry vets.
Mudbox is Node based. This is a huge. This will be an incredible asset for years to come. This will give Mudbox some great speed, this could also help give users lots of options. Mudbox was designed and constructed by industry artists, for industry artists. Software that has had this at its roots has faired quite well, (I.E Shake). I’m not familiar with Pixologics background.
I would say, both are great, right now I think it will be like the last great years of Illustrator vs. Freehand. One person would say the other was way ahead, and someone else would say the other was way ahead.
Either way, we as the consumer win. I’m glad to be able to make a choice. For me, I’m just waiting for my Mac Z3 upgrade.