It'll generally work, but there are caveats that you didn't list:
1. The investments inside 529s in most cases have higher expense ratios than equivalent investments inside a Roth. This will offset your $750 matching bonus.
2. You can just put the money into your Roth now and it's a lot simpler and probably just as tax advantageous. It's pretty hard to come up with scenarios where you have extra income that you'd like to put into your Roth now, but are willing to wait 15 years, and then will have includable compensation but not be able to fund a Roth contribution at that point. And even then, the whole scheme is limited to $35K anyway.
And I'm not sure I understand your comments about lowering AGI. Contributing to a 529 will generally reduce your state taxable income, but doesn't have any impact on your federal AGI. And contributions to a Roth, either directly or via the new 529 -> Roth rollover mechanism also do not reduce federal AGI.
Lots of people are trying to take advantage of this new mechanism in the law. Understandably so, it's a cool law and could be an opportunity, and I'm always looking for loopholes. In this case, I think the law was written narrowly enough that it benefits the intended audience (parents who overfunded a 529 or who are worried they might). But it doesn't really benefit anyone else or create any sort of particularly useful loophole.