I am writing an Android app which needs to be run on BlackBerry Z10, too. Someone mentioned that Android apps can be wrapped for BB. However I am not sure of the version. If I use 4.x specific features, e.g. swipeable tabs, will they be supported on BB, or should I use some older API, e.g. Eclair (2.1) to be on the safe side?
I just want to program once, and not twice.
Today, you should build your Android apps to OS version 2.3.3 (API level 10). So, you should produce a version of your app that doesn't use features in newer API levels.
Here is the official BlackBerry page that mentions this:
You can use the BlackBerry Runtime for Android apps to run Android 2.3.3 platform applications on the BlackBerry Tablet OS and BlackBerry 10. To use the runtime, you must first repackage your Android applications to BAR file format, which is the compatible file format required for an application to run on the BlackBerry Tablet OS and BlackBerry 10.
Update: it appears that BlackBerry has a status page here, detailing their roadmap for Jelly Bean support. Of course, every device won't support it the day it comes out, and BlackBerry has missed deadlines before. But, it's probably good to keep all those things in mind when planning your project.
The right decision for you will depend on how long you expect your development to take (2 weeks, 3 months?), how important the features are that depend on 4.x APIs, how much you're willing to assume BlackBerry meets their schedule, and how important a strong launch is to you. If only a small number of devices are actually upgraded to support Jelly Bean when you release, it may hurt your sales.
Anyway, the point is that it depends on a lot of factors. Hopefully, I've described most of the important ones.