We have basically three categories of apps: entertainment, social, and productivity. In general, only productivity apps are able to generate platform lock-in: entertainment is consumed, and rare are the games that keep our imagination for more than a few months, while social depends on providing the largest audience and so has a very strong incentive to be cross platform.
This makes productivity apps extremely important for platform owners, but we can see on the Apple App Store that they are playing second fiddle to games. The problem is that for such apps to thrive, they need recurring revenues, so that they can be improved to stay relevant, while the store has grown from selling songs, and so lacks upgrade pricing, and especially mechanisms to check out apps before committing to them.
I wonder what Apple’s thinking about it is. The complaints have been known for years, and not much has improved. Apple continues to dominate the productivity category with excellent apps sold for relatively low prices, and one wonders whether Apple is afraid of dominant apps emerging on the store, having been burnt when Adobe pretty much abandoned them for Windows.
This means that you need to work around a relatively hostile environment when you want to sell productivity apps into the mass market. The only category working well already are tax preparation packages, as you need a new version every year to follow tax changes, so it makes prefect sense to sell a new package every year. For all other software a subscription model would work best, but it is only tolerated as long as you have a server component with it as well; also there is the issue that customers do not want to pay a permanent rent to be able to access their own files.
What to do now
The only way you can get a trial version into the store is to provide a full version that can only handle one document (or for social apps be limited to 10 contacts). If this does not fit your app, your only chance is to provide a good video demonstration on the app website.
Upgrades are not supported, so you will need to put a new version into the store, and inform your old customers with a notification that the new version is now available, and that for the first weekend it is on sale to ease upgrades. This should be the only sale you are doing, so that people are not starting to wait for the price to drop again.
What Apple can do
Everyone would love to see upgrade pricing, but I doubt that Apple will provide this: they want software to move to the newest iOS for "free", so that users can easily upgrade to new hardware.
A great help would be the ability to provide upgrades to apps no longer on sale, as long as the same app is also made available for sale on a different sales ID. This would enable a slightly longer support cycle: For every major iOS release you put a new version on sale, and remove the older ones from sale. You provide the current version as an update to your old customers for two or three additional iOS revisions, before stopping with updates. Once you have provided your last update, say for 6.1.3, and 7.0 is out, you could then put the old version back on sale for old devices, with a clear statement that it will not see any updates anymore.
There is also quite some room to improve app discovery on the store, enough to warrant its own post later.