I've published a few apps on the Google Play Store and there are a few things that would drastically improve the experience for developers.1) Add a promo code system
This seems obvious to me and is something that Apple does decently well. I'd love to be able to give premium versions of my apps for free or for a discount. I could run Twitter promotions or create contests on Reddit to gain a user base. I wouldn't mind paying Google their 30% cut for each code.
2) Better Alpha/Beta system
Google Play already has an Alpha/Beta system which is run off of Google+. Basically they are closed betas and a user has to sign up via Google+ to gain access. This has a few benefits - but honestly if you don't already have a decently large following on social media, it is pointless.
Google could provide an open Alpha/Beta system which lists the app on the Play Store as they normally would, but the app would have an Alpha/Beta tag next to the name so that users know what they're getting into. Disable comments and ratings during this period so the app isn't negatively impacted in the long-term by early bugs.
3) Better in-app testing for non-consumable items
In-app testing is surprisingly easy to implement, and ridiculously difficult to test thoroughly. Basically, there are two types of managed in-app purchases on Android: consumable and non-consumable. Things like "Add 100 credits" can be purchased many times, so that is consumable. Things like "Upgrade to Premium" should only be purchased once, so that is non-consumable.
It is very difficult to end-to-end test non-consumable in-app purchases in Google Play. For some reason, developers cannot purchase their own items when their app is signed - not even a test purchase. Not really sure why Google prevents that.
So in order to end-to-end test your in-app purchase, you either have to ask someone else to do it or you have to format a device, sign up with a Google account other than your developer account, and test it that way.
4) More flexible subscriptions
Subscriptions are either monthly or yearly. This means the cheapest subscription models are $0.99/yr and $0.99/mo.
We all know that charging for apps is hard - and finding a price point is equally as hard. The problem with subscriptions here is that for apps that provide enough value to justify charging a subscription, $0.99/yr sounds too cheap and $0.99/mo sounds too expensive.
Adding a quarterly option for subscriptions would work well for apps I think. $0.99/quarter sounds better than $3.99/yr. I'd be willing to bet quarterly subscriptions would outperform both yearly and monthly subscriptions where the yearly price points are all equal.
5) Variable ratings based on app version
I think app ratings should be variable based on app version with ratings on more recent app versions having a higher weight than ratings on older app versions.
If your app is currently v2.0, ratings on the 2.0 version of your app should be worth more than ratings on your 0.1 version of your app.