The TechCrunch article says, "Apart from the fact that Mozilla had cut off most development support in 2012, Thunderbird has become a somewhat anachronistic product." For any enterprise or business environment where email still rules, calling Thunderbird "anachronistic" sounds misinformed and insulting. Thunderbird may not have the market share of Outlook or the glamor of smartphone based mail apps, but I'm sure those who use Thunderbird are really passionate about what it provides and the extensibility that comes with it.
One of the things I don't like about the Mozilla of the past few years is the high amount of effort and time spent on Firefox OS. I don't want to put that down, but Mozilla is trying very hard with very less traction on it and still pushing onward.
Mitchell's message sounds like more planning is in the works to separate Thunderbird and probably make it stand on its own. This will take some time to plan and execute, with Thunderbird just languishing in the meantime. There could also be a complete re-write of Thunderbird, which is not really a great idea. I can see both optimistic and pessimistic views on what the future holds.
When Mozilla Messaging was announced, I had high hopes for better integration with Exchange calendaring and also improved search. All that went to nothing in 2012.
If Thunderbird ends up as a separate entity that I can donate directly to, I'll be one of the first to do so!