Just as an example let's say "q", followed by a space, followed by the command with the appropriate number of parameters, e.g., "q get username". That would allow otherwise-reasonable tweets that are currently being mis-interpreted ("get better" vs. "q get better").

That's just an example. There are other ways around the problem too without making things too inconvenient on a smartphone user. And sure it's possible someone somewhere will want to write a real tweet that says "q get better", but that's far far less likely than someone somewhere wanting to tweet "get better". And the point is that allowing a non-trivial portion of the tweet-space overlap with the command-space is a bad decision. A trivial overlap (like "q get better") would have been a much better decision.