Well, one thing might help. Persuade the Haiku devs to bundle the yab executable with Haiku itself, just like python. That way yab devs can upload their apps as chmodded scripts rather than as enormous "bound" bundles. Uploading most of a meg to haikuware (this is from memory, it's been a while) for a little 100-line utility gets old fast.
Truth is, yab is unique: a strictly procedural language that can be used to write (modest) GUI applications. No need to bend your brain around object orientation. No need to keep track of a thousand libraries, it's all there in the one executable! I've found nothing else like it anywhere, on any OS. Applescript, maybe, but finding documentation on using that for anything but office automation is a lost cause, and even Apple has been neglecting it.
I was so fond of yab that I kept coming back to Haiku just to be able to work with it. But ... well, no need to go into details. Let's just say that I haven't fired up my Haiku box in months, and I come back here once in a while out of nostalgia.
There used to be a project called flyab, which was supposed to bring a subset of yab to other OS's. Perhaps that could be revived. Make it cross-platform and you'll attract a whole lot of new people, at least some of whom will try yab on its native platform.
But even if that is asking too much, if the Haiku devs could bring themselves to embrace yab and bundle it, it just might give Haiku itself a boost. Back in the Windows 3 days, you needed one file: VBRUN300.DLL, and suddenly you had access to thousands of apps. They might have been slow and buggy, but they existed. A year later, DOS was dead and Windows was everywhere. Yab could do the same thing for Haiku.