Glad to see you're back!
I agree on IPv6 being the future, however I wouldn't quite hold my breathe yet on it. While support for it has been widespread in the last several years, very few places put it as the priority in their web applications and software. Likewise, ISP's are relying heavily on IPv4 addresses being constantly reused, (dynamic IP's are very common now on residential internet services), so they will probably fight to the death on keeping IPv4 as the main standard until it simply cannot handle the amount of devices anymore. (Think of it like the Y2K panic where everyone waited until the last minute to update their systems to support the new millennium rollover. I see something similar happening with the IPv6 takeover).
That being said, I personally welcome the idea of IPv6 support being added, but I completely understand your reasoning behind why this has been held back. (Project Honeypot and Stop Forum Spam need to get on this!)
As for SMF 2.1, I'd absolutely LOVE it if httpBL and StopSpammer supported it. Right now I'm running my 2.1 forum without any anti-spam mods simply because none exist. Your mods are hands down the best I've seen, and definitely the most effective. On my old 2.0.x forums elsewhere, I used to couple them with a group of other miscellaneous anti-spam mods that queried smaller databases just so I could catch the few rare ones that slipped through, (and boy were they rare). If 2.1 versions existed, I would install them right now. These mods are absolutely incredible. Please, please, please add 2.1 support!
On a side note, your mods are so effective that even my PHPBB 3.1 forums use similar mods to query the same databases, that's how much I believe in them. Your SMF versions still blow the PHPBB equivalents out of the water too, and I've been using both forum softwares for a very long time.