If you use the syntax highlighter you cannot see what you post will look like until you actually posted it.
It would be nice to have a preview so that you can correct posts before actually saving them.
The ABL brush within our Community is a "non-supported by the vendor" add-on we implemented on top of the tiny editor. Being able to preview may require additional custom code that could eventually break a few other stuff and therefore we can't make that happen... Sorry.
Agree, I don't use it very often, but when I do, I always think it doesn't work. Until I give up and post it anyway, only to discover that it works after all.