Please note that I was not referring to technical complexity, rather cognitive / UX complexity. I've been creating software for many years, I'm well aware that

Please note that I was not referring to technical complexity, rather cognitive / UX complexity. I've been creating software for many years, I'm well aware that feature requests that look quite simple on the surface can require significant development efforts. Having said that, implementing trials / upgrades is no a technical problem per se, it's more a question of spending the development resources required (yes, obviously there will be assumptions in the whole infrastructure that would require a bit of work but nothing that should have taken years to implement). In-App-Purchases were introduced a few years into App Store's existence, so it's certainly possible for them to implement major features when the willpower exists (and I'd wager implementing trials / upgrades would be easier than IAPs, although that's my guess, I have no internal information). In any case, I very much doubt the reason for not having those features implemented is because they don't have the available development resources - it's more likely a decision was made that those feature do not align with Apple's vision of how the MAS should work.