It is quite possible that some trade-offs which held down the growth of intelligence are no longer operational and humans can/will continue to evolve towards even higher IQ.
Maybe, but as you say, it would come at potential cost. E.g. gain of a few points but you won't survive famine, that doesn't sound very good.
Or much more insidiously, gains on an IQ test, at the expense of ability to form/organize/use complex background knowledge (IQ tests are designed to be minimally affected by extra background knowledge).
Practically, of course, the point is moot as evolution is very very slow and humans will self-modify much more rapidly than evolution could provide any noticeable gains.
Yeah, either that, or the civilization goes kaput and it's back to all-natural selection.
A long blog post explains why the author, a feminist, is not comfortable with the rationalist community despite thinking it is "super cool and interesting". It's directed specifically at Yvain, but it's probably general enough to be of some interest here.
http://apophemi.wordpress.com/2014/01/04/why-im-not-on-the-rationalist-masterlist/
I'm not sure if I can summarize this fairly but the main thrust seems to be that we are overly willing to entertain offensive/taboo/hurtful ideas and this drives off many types of people. Here's a quote:
The author perceives a link between LW type open discourse and danger to minority groups. I'm not sure whether that's true or not. Take race. Many LWers are willing to entertain ideas about the existence and possible importance of average group differences in psychological traits. So, maybe LWers are racists. But they're racists who continually obsess over optimizing their philanthropic contributions to African charities. So, maybe not racists in a dangerous way?
An overly rosy view, perhaps, and I don't want to deny the reality of the blogger's experience. Clearly, the person is intelligent and attracted to some aspects of LW discourse while turned off by other aspects.