No. Not unless there's a good reason for doing this. Whatever threshold you add to signing up, even if it's only temporary, it's gonna drive some users away who could've become great and valuable contributors. I think there has to be a very good reason to do this. Currently it's a solution looking for a problem. One reason I could think of that might be worth it is to prevent a massive flood of users. I quite like nowaypablo's idea of a time delay - it's much more egalitarian than invites. A measure that might work against floods of users is by making the delay dependant on site traffic. On a quiet Saturday, it might take just ten minutes, whereas on a busy Reddit flood day a user would have to wait a day or two to be allowed into the site. That way it won't have an impact 99% of the time, and will have an impact when it matters.Is it worth an experiment?