I sent in a question to customer service and they came back with this message:
"We do not currently have any plans to develop an Ancestry.com application for Android smart phones. However, we'll pass your suggestion on to our programmers who will consider the idea for future implementation. We apologize for the inconvenience."
... so it looks like its not going to happen unless Ancestry have a change in plans. I suggest anyone who wants it sends a message into Customer Service. If there is a demonstrated demand perhaps they will change their minds (which seeing the ubiquity of Android seems to make commercial sense)