We at the Acquia DrupalGardens team were recently thinking about how to solve the problem with style attributes being blacklisted by core's HTML filter. It seems to be a choice between wysiwyg_filter and HTMLPurifier. We'd prefer to use your code as it seems more robust, tested and applied elsewhere.
Indeed, I'd like to see it replace the filter we have in core. I think the fear is performance. Do you have any benchmarks on using HTMLPurifier? Do you feel like it is performant in varied situations (lots of text, many transformations per page load, etc)?
We'll probably need to start on a 7.x port ASAP if we can prove the performance will be good enough. Also, are you interested in doing any (paid) work on this? Please get in touch if so via my contact form or here on this issue.