I think most developers would be behind it as well. Maintaining a separate paid and free version was a pain in my ass. If you do it right it's pretty minor to build your code with different compiler flags for each version, but you still have to do every build twice, upload to Apple twice, manage version change descriptions twice, and so on.
Developers have been asking for Apple to officially support trial versions for years. At this point I have to assume it's either a patent minefield they can't figure out how to get around, or Apple thinks it's a bad idea and will never implement it.
I can't speak for all users of the App Store, but personally, if an App is more than $1, I really debate whether or not it will live up to its claims. So many apps are bogus, crash, don't live up to their promises, etc. I'm betting if developers were able to offer their apps for a 24 hour time period as on Google Play, that it would greatly reduce the number of crappy apps & developers who flood the app store with garbage. People would just continually refund their purchase and they wouldn't make any profit.
It theory it should increase the integrity of the apps..