FWIW, I had emailed a similar question directly to SPB at the end of March and here is the reply I received at the time:
Thank you for your message and interest in SPB Software.
SPB Mobile Shell was just announced. Unfortunately, we do not share information concerning our release dates because of the internal policy of our company.
You can subscribe to our product updates email to know as soon as SPB Mobile Shell version 5.0 is ready:
Feel free to contact us if you have any additional questions.
Since they announced this way back in mid-February and have never provided an update since, I guess I'm not holding my breath. A shame -- I used this in my Windows Mobile days and liked it, although I'm still waiting to see how it would make the "paradigm shift" from WM to Android with their somewhat different home-screen designs. Since support for multiple home screens was one of the key advantages of Mobile Shell but is built into Android, I'm wondering how much added value the SPB Shell would provide. They also had some nice built-in widgets as well as cool visual effects like the rotating carousel (similar to what's already available in the GDE Launcher).