Official support would be nice, but can't developers already implement trials using in-app purchases? Download the app for free to get the trial, then pay to unlock the full version. Many apps are already using this approach.
Say you have an app, Foo. It's a reduced-function version and you want your users to buy Foo Pro. In order to use in-app purchases as an upgrade mechanism, you now have a bunch of customers running with Foo, except with Foo Pro functions unlocked. And you also have a bunch of customers running around with just Foo Pro.
The second part of this mess is that, unlike app purchases, users cannot see which in-app purchases they already own. If they ever get a new device, reinstall the app, etc etc, they have to "buy" the in-app purchase again to unlock the Pro version, and pray they don't get double-charged (it happens). As an app developer this is a support nightmare scenario.
This is not to mention that some users will mistakenly purchase the Pro version (and thus get double charged) when they get a new device, instead of downloading the regular version and "re-buying" the in-app purchase.
Yes, I did not know this. I don't understand the reason behind this rule, but as a user I find time-limited trials annoying. I prefer to have a trial version where I can use all the functionality but with a limited amount of data. For example, a task management app may restrict the number of tasks I can create. This way, hitting the limit is a good indication that the app is useful for me. Hitting a time limit doesn't actually mean anything, while crippling the functionality itself means I can't really try out the app.
> you now have a bunch of customers running with Foo, except with Foo Pro functions unlocked. And you also have a bunch of customers running around with just Foo Pro.
What I suggest is to not have Foo Pro at all. Just one version, Foo, which is free and can be unlocked.
> The second part of this mess is that, unlike app purchases, users cannot see which in-app purchases they already own.
I agree this is a mess, but remember that not too long ago there was no way to see app purchases either. So there is some hope this information will be added soon.
One only has to look at how it works for Xbox Live Arcade games for an idea on how seamless this is. Give the user enough so that just as they are hooked, the trail runs out. One click of a button is the entire upgrade process. No dumping out to a different application (Marketplace) in order to purchase the full game, just a one second click of a button.