(Just as a note, this would probably require substantial update.) I would like the option to have a monthly calendar built into the app, with the option to schedule upcoming study vectors and check them in advance. The calendar could also have little stamps on days where you meet your study goals (daily review, heatmap, personal goals for new terms, etc.)
For the general functions, it would be nice if we could click the days on the calendar to access a side-bar (or different menu) with the daily study goals. It can have your daily review goal set by default, plus the option to add your own schedules to the goals. (E.g. I make a new daily study goal, select a Renshuu study schedule, and set my goal as 5 new terms a day.) A stamp is added when users have met their daily goals. The stamps should only serve as a visual indicator of one's diligence, sort of like the heatmap but personally-driven instead. Obviously, there would be no negative repercussions for not meeting the daily goal.
(Please let me know if you need a better explanation or some visual mock-ups.)
I'm not sure how Renshuu's schedule system works, but it would be great if we could also set up a consistent study schedule through the calendar feature. There could be study parameters such as "[number] new terms every [day, weekday, month, etc.]" This could give users some measurable goals to work towards throughout the week or month.
This sounds like an amazing idea! Unfortunately, it's far beyond what I can consider in the near and not-so-near future. You are correct - it would be a huge update to make this work (and keep it simple enough so that renshuu is not even more complicated than it already is from the perspective of new users).