Twitter wants to register TWEET as a mark, but they’re planning to peaceably coexist with those who use the mark in the same commercial space as Twitter does.
First of all, they haven’t been using TWEET as a mark. TWEET, in the Twitter world, is a noun; trademarks are adjectives.
Second, their proposed use flies in the face of US trademark law and in the face of trademark usage. Trademarks are in place to protect the public from confusion as to the source of goods and services in the stream of commerce. If the mark is used by many to describe goods and services for many sources in the same commercial space, the public will be confused as to the source of goods and services sold or marketed under the mark. Thus, the mark would not be usable as a trademark is intended to be used.
Sorry, Twitter. If I were the examining attorney on this one, I’d deny the registration of the TWEET mark based on genericism. That’s what your own strategy makes of it.