That may work in some cases but for QA reasons alone it gets unsustainable really quickly. Let's say you have your base app then "Upgrades" A, B, C.
* What if the user buy's C but not A and B?
* Does B/C rely on anything in A or C rely on anything in B
* For every upgrade the dev needs to test all the possible combinations of upgrades bought by the user
* Positioning for new UI added by A/B/C dependant on what other upgrades have been purchased
You might be able to solve most of these with requiring A for B and B for C but even then you still need to test your app: Base+A, Base+A+B, Base+A+B+C......
* What if the user buy's C but not A and B?
* Does B/C rely on anything in A or C rely on anything in B
* For every upgrade the dev needs to test all the possible combinations of upgrades bought by the user
* Positioning for new UI added by A/B/C dependant on what other upgrades have been purchased
You might be able to solve most of these with requiring A for B and B for C but even then you still need to test your app: Base+A, Base+A+B, Base+A+B+C......