Yay for an improved TagTime app.
Are you using the TagTime algorithm?
The timer view you have on the main page makes no sense for this, as it's important you not know when the pings are coming.
Tag history, I'm not sure what the point of the Day/month/Year filter here is.
I have a lot of ideas about this, I've been tagging 24/7 using the Android tagtime app for more than a year.
Make it easy to add tags.
Make it really easy to repeat the last set of tags.
Use some magic to provide relevant/related tag predictions. (based on both time and recent tags.)
Not sure your proposed tag picker will be good, I have ~500 and I'll never be able to find them on 1 horizontally scrolling line.
Easy searching of tags
I want to report only the relevant tag(s) to beeminder, currently it adds all the tags added at the same time. (Some people probably want this too though.)
Use Boolean Tag combinations here too.
Want submission URL to be configurable so I can submit tags to something that isn't Beeminder if I want to.
Needs graphs so it's not necessary to export data to get value from it. (current Android app lacks this)
I want to be able to graph tags, tags with boolean logic (Web && !Work)
Want to be able to graph multiple things on the same graph (Sleep, Work, Family)
Reporting based on periods. (between dates, last month vs this month, last week vs prior week)
If you're planning on making it open source and on Android I can help with development and testing.