[Note: I can't read the original link -- the site is down -- so I have no idea what the original submitter said. But let me take a guess about what you're saying.]

Try to put yourself in Twitter's shoes. Your viral app is a fantastic, unprecedented success. Your traffic is doubling every week. The Fail Whale is onscreen so much that it has its own name, its own fan club, and its own T-shirts. Techcrunch is rumbling about all the other entrepreneurs who are setting up to clone your service.

The idea that a language-level change to Ruby is a wise thing to pursue at this point is insane. Ruby has a big and complicated code base. You are not a language designer. You probably won't even figure out what you could do that would help. If you do, the change will probably result in an internal-only fork of Ruby that can't be reliably patched and that is incompatible with a random cross-section of your third-party libraries. Deploy that thing and you will be finding and fixing Heisenbugs all over the codebase for the next six months.

To actually get an official change into Rails takes months, minimum. In the case of Ruby that might stretch into a year or two. Because you must first win a series of online arguments, and then you must wait for lots and lots of third parties to test your change against their apps and libraries and report or fix the bugs.

Yep, much cheaper to just rewrite your whole stack using different infrastructure. Several times, if necessary, as experiments. Twitter is expert at rebuilding their own stack -- what has been done before is easier to do again.