An option for having the streak be able to add a streak day for every day reading, rather than only every however-many-days-you-set.
So if you read the quota every day, you add +1 for every day. The days-set just acts as a buffer to not lose the streak.

So my streak is every 2 days, but I wish every day that I read increased my streak and that I could just have 2 days as the grace period before I lose it
but as it is I can only increase my streak every 2 days

ie. mine is 10 pages every 2 days
So if I read 10 10 0 10 10 10 10 0 my streak would be 4 at the minute
But I'd love it if that worked so that it would be a streak of 6

It would be really cool to see the average amount of pages read (and/or minutes listened) over an amount of time - for example over the last 28 days as part of the streak page.
I’ve worked out that to reach my pages goal for the year, I need to read 50 pages a day, so an average would be helpful to see that I’m on track.
I feel like this would fit into the streaks quite well :)

I'd love to see a split between pages and minutes streak (if applicable) — what's my longest pages streak, what's my longest minutes streak, what tends to be the average number for my streaks in both cases.

In my case specifically I log a bit daily no matter what so I would love to more insight into what makes me log more or less and when, since my numbers vary a ton; but I realise that's a minority, so prioritising what makes people log at all likely makes much more sense!

I really like the suggestion jaina8851 left below, so based on that — no idea how doable it is, but you could have a machine learning-powered carousel saying, "You're more likely to have a streak when you're reading books that are [genre, mood, length]. How about adding some of the books below from your TBR to your Up Next?"

Compare stats to other plus users! Like "You read more books than 10% of Plus users" or "You reviewed the most books this month"

A calendar version would be nice to have visually!

These are only half-baked ideas haha...

This one probably would be data storage intensive, but like... some kind of comparative historical streak data might be really cool. Something like "your longest streaks tend to be from late December through February, with an average quit date of Feb 21, can you break your record this year?" or "here is a graph showing all streaks longer than X days" with a hard minimum of whatever makes sense from a data performance perspective but maybe an otherwise customizable number. Attaching a super rough graph idea for this. Might be tricky given how delightfully customizable the notion of what constitutes a streak is, but, just a thought.

Another idea would be comparisons with other users... like "here's the bellcurve of streak length, here's where you land".

Or what about correlating some aspects of the journal entries with streaks... "you are most likely to maintain a streak if you're reading X genre or mood".