I’d very much like to adopt iOS 13 as a minimum system requirement
Not officially, but some users have had success running our Android app in various emulators on desktops, and newish Chromebooks support running Android apps officially through the Play Store so if you consider those to be 'desktops' that would be a desktop version.
Also, we are hoping to launch a macOS app later this year when Apple releases a macOS update with their new "Project Marzipan" allowing iPad apps to be easily recompiled to work on Mac.
Until 4.0 is finished on both iOS and Android we don't have the available staff time to do a PC port, and there's not really any amount of money that would cause us to reorder our priorities to get a PC port of 3.x out before that. Mac port can happen sooner since the work on that can happen in conjunction with work on 4.0 for iOS, but a PC port is a totally new thing.
That makes sense.
I don't know much we'd ask for if we decided to crowdfund a PC port - quite a lot, I'd think; I remain highly skeptical of the commercial potential for a PC version of Pleco, so we'd have to make enough money to not only cover the cost of the initial port (with the inevitable delays / complications) but also let us maintain it for a while even if post-release sales proved disappointing.
We don't list on Amazon, but actually that's not necessary; per this tweet from Miguel de Icaza at Microsoft, you'll be able to load APKs on Windows without the Amazon AppStore as well, and we already offer Pleco as a downloadable APK.
Honestly I think the Amazon integration may have a lot to do with the fact that while the Amazon store is kind of a ghost town in general, by virtue of being the primary app store for Amazon's Fire tablets it does have a lot of tablet-optimized apps (which should therefore scale well to large screens).