The email Sparrow is sending out, looks like there won't be any future feature additions:
Hello,
We're excited to let you know that Sparrow has been
acquired by Google! You can view our public announcement
here, but I wanted to reach out directly to make sure you
were aware of the news.
We will continue to make available our existing products,
and we will provide support and critical updates to our
users. However, as we’ll be busy with new projects at
Google, we do not plan to release new features for the
Sparrow apps.
It’s been an honor and a pleasure to build products for all
of our wonderful users who have supported us over the
years. We can't thank you enough.
We look forward to working on some new and exciting
projects at Google!
Dom Leca
CEO
Sparrow