There's a lot of low-hanging fruit there. They could copy some Play Store features such as:

* Auto-refunds if you delete the app within 15 mins (this de-risks the app purchase)

* Suggestions for apps that your friends have used

* Better search

Other non-play store often-requested ideas:

* Don't disincentivise upgrades by zeroing out your reviews when you upgrade.

* More reasonable app reviews.

* App subscriptions instead of up-front fees (eg pay $1/month for each month where you use my app more than N times).

* Better curation of the app store (eg don't only feature games).

* Before allowing 1-star review, suggest the user should contact the developer and give 24hrs for a response.

* Allow users an option to either post a review or submit a public question.

For reviews, we tried a more checklist-like model in the Maemo Downloads store back in the day. You had yes/no questions like "does the app do what it claims to do".

There seems to be a negative reaction to apps using IAP as a paid upgrade, though.

I, personally, like the business model as long as the app is very clear about what is offered with and without the IAP, but I have rarely seen a review mention this practice favorably.

IAPs do not share within a family. That's a big problem maintaining five or ten devices.

It already has paid upgrades via in-app purchases. Upgrades, both one-time and subscription are explicitly supported. Trials are a bit of an issue, though, but it's quite possible for an app to offer the upgraded experience free for a limited time.

True, but conceiving and building the right IAP structure takes substantial time and money. If there were some sort of trial system that all customers could use to try out any app, then some app devs (not all) could ship apps much more quickly. I know we spent a ton of time figuring out what we should offer for free, what we should charge for, and how we should draw a line between the two. If there were a 15-min trial we would have just used that and not worried about it. (And if you're wondering why we didn't simply implement a 15-minute timer in our app, it's because people would have thought it was weird, since pretty much no other iOS app uses that. But if it were standard, this wouldn't be a problem.)

I suspect trials would lower revenue rather than increase it, all those impulse purchases would go away.

I think this is an important factor. I am quite willing to pay $3 for an app that looks cool enough that I want to try it out, but wouldn’t pay $30 without trying it first unless it comes very well reviewed.

Is it better to have the revenue for one $30 purchase after a trial or 10 people who impulse purchased it for $3?

Trials might be important for apps that need to cost $100 or $500, but for more reasonably priced apps it is not totally obvious that they would make a huge difference. Maybe for some categories of apps like those targeted at kids who would need to convince a parent to approve the purchase, and in fact games tend to be free with IAP.

Easy paid upgrades seem like a bigger deal.