Here's an off-the-cuff prediction: Twitter itself, as well as the Twitter community, will be just fine. In a year or two nobody will remember these problems.

Twitter may have scaling problems, but it's not as if their potential competitors are magically immune to those. Meanwhile, Twitter holds a huge marketing advantage -- you can't say "Site X is just like Twitter" without saying "Twitter" -- and a big Metcalfe's Law advantage: Everyone who is remotely interested in Twitter-like sites already has a Twitter account, and those accounts won't magically disappear. Meanwhile, there will be more than one Twitter competitor, all desperately trying to distinguish themselves from each other as well as from the original.

Sooner or later Company X will figure out how to scale Twitter. At which point either Company X buys Twitter for the name and the userbase, Twitter buys Company X for the technology, or Google buys everybody. Or, Twitter eventually reverse-engineers the superior architecture, at which point they will beat Company X over the head with superior name recognition and larger userbase. This is especially true if Company X is actually the open-source community -- if some random Python programmer manages to create a superior, open-source Twitter architecture, Twitter will just install it on a server farm within a month and be right back in the game. The open-source movement has a lot of brilliant techies, but I doubt that its marketing team can outrace Twitter's from a standing start.

The Twitter concept has enough mindshare that I doubt it can just evaporate. They're not being sued out of existence like Napster. I'm not convinced that a scalable Twitter is physically impossible. So I would suggest that rumors of its death are greatly exaggerated. It's just... resting.