I'm not supporting 1.0 plugins because I don't feel like it. That's the reason. It is too much of a pain to support multiple paradigms.
Really, if I could, I wouldn't even support 1.2 plugins, but that'd destroy the current userbase and I don't want to do that.
imo i don't think you should need to support 1.2 plugins, atleast not at release, let people get a headstart at developing and converting 1.2 plugins and release it on WoWInterface.
Oh and i lost my settings agains and i found out that overflow panel is bugging out, after the first plugin has overflown and created a new panel then it will create a new panel for each new enabled plugin. Don't know if that's an issue with 1.2 plugins or not though.