JPEG XR is actually quite good and is now an open standard. I recently did an extensive evaluation of JPEG 2000 vs. JPEG XR. While JPEG 2000 has slightly better compression quality (less visible artifacts) at the same file sizes it’s decode performance is substantially slower than JPEG XR (the same is true for encode performance, but decode is much more important). In my testing, one of the fastest JPEG 2000 libraries, Kakadu, is anywhere from 1.8 to 2x slower than JPEG XR at decoding files. Kakadu is a commercial framework, the open source OpenJPEG library is supposed to be substantially slower.
Compared to standard JPEG, JPEG XR has on average the same or very similar decode performance. The bottom line is that with JPEG XR you get compression quality and file sizes that are similar to JPEG 2000 with performance that is similar to standard JPEG. In my eyes, it’s the best successor available to replace JPEG. But it has a long uphill battle ahead of it.