I agree that it's a risk, because there are potential readers who simply don't like it and won't read it. But well, that's probably on the same level as deciding to write a weird femmeslash pairing - in-built smaller audience :).

Agreed with your AU definition - well, that's how it's defined in my book, but the terms AU and AR seem to be pretty much used interchangeably.

The story itself - just a matter of tying right into the end of OotP with Lucius out of Azkaban... not such a big thing (I shouldn't leave stuff unfinished for years!).