Do you think Apple would endorse such a product?
Apple has accepted Mono applications to the App Store, which is as close to "endorsed" as you can get.
I'd just like to add some perspective to this thread if I may — I'm a software developer for Mac by trade (photography is a hobby) so hopefully I can be useful.
Mono is no less "native" than 90% of Mac products out there. A lot of people think "Native" means "Written in Objective-C against the Cocoa framework", but that's just one of the many tools available to make applications for Mac OS — it just happens to be the one Apple provides. However, many of the applications people on this forum will use day-to-day aren't written using these technologies, for example:
- Microsoft Office
- Adobe Photoshop, Lightroom, etc
- To be honest, pretty much everything out of Adobe ever
Having a common codebase when your application runs on multiple platforms is the best way of doing things, not just because of cost — if you have multiple codebases for multiple platforms, you can guarantee that the core functionality of each version will be slightly different, and you have to spend a lot of time making sure the separate implementations are compatible with each other as well as weeding out more bugs, etc etc.
However, since Mac OS, Windows, and other platforms have very different looking UIs, this normally leads to a sub-optimal product UI-wise, since to make something work on everything, it ends up being a mashed-up compromise. To counter this, products will often have a common "core" while implementing the UI separately for each platform. It is absolutely
possible to make an application in Mono that doesn't look "ported", but it takes more effort than using a UI that works on all platforms. And, looking at the software in question, the UI is so simple that it doesn't need
Edit: To put things in perspective, Adobe products use a common UI layer on both of their platforms. They went full-in and designed their own UI toolkit that works fairly well on both platforms, but can be frustrating to use on a Mac since it doesn't entirely conform with standard Mac behaviours.
Simply put, if this application isn't "native", neither is Office, Photoshop or Lightroom. And, well, they're all damn fine products. Furthermore, I bet if they'd included Mono inside the application package rather than requiring it be installed separately, nobody would have even noticed that this application wasn't "native".
As for Mono being bloated, well, the install size of the runtime is around 300MB. If you look at the size of Apple's libraries you'll find they're a lot larger than that, it's just that they come with the operating system so you don't have to download it.