I think it depends on why the writer is using old canon. If they were doing it to comply with the terms for a specific challenge, or if it's something that they started writing and plotting before HBP came out but they're only just now posting it, yeah, I'd read it. If it's because they hate HBP or OotP and are aggressively in denial about it -- well, they're entitled to their opinion, but my opinion of the canon is so different that it's unlikely that I would enjoy their writing.