Edit: There's really only one way all you asked in the OP can be done, BTW, and it is guaranteed to be more resource hungry than SMF, because SMF isn't designed to do all those things, and the way you need to structure the code to do it will be a bit slower. But not by much.
This is definitely not true. SMF is written in PHP, and it has a lot of unnecessary inefficiencies (which I've been fixing to keep the forum running). The additional features that I require aren't very resource-intensive, and I don't require some of SMF's resource-intensive features. The most expensive required feature is the web of trust, but that isn't too slow to begin with and it can be made faster with caching.
Maybe it's impossible if you write it in a week using bloated frameworks...
Simple question, if you had a system exactly as you described except that it was 30% slower than SMF, but say, could be run on multiple servers to scale very well, would you take something like that?
The slowness doesn't bother me much if more hardware can fix it and if the slowness doesn't increase exponentially with more users. However, if you know in advance that your design will be 30% slower, then I probably won't like your design for other reasons. I don't like doing too much at runtime for the sake of coding convenience, and I do like SQL.
