The number of tokens the site had (forgot what it was) before the final API changes that limit tokens was rather high. It was well over 100k and based on Twitter's rules, any app that had over 100k tokens would be able to go to 2x that number. I believe the app had somewhere around 600k tokens at the time so there's still some room for growth. Though the plan would be move from solely Twitter-only to something covering more social networks or create its own network. Not sure yet.
He said he said it up before they imposed their API limits. So I suppose all pre-change signups remained and it is likely that the OP is unable to signup any new users through the twitter API.