Debian/Arch are both fairly lively, if you want something battle hardend you'll use SLES like Walmart, Kroger, Fred Meyers, Vons, <Fill in major retailer> uses. The desktop is in stasis though, and iOS as a platform is unlikely to grow massively over the next few years.

Android is frankly another rotting cesspool of Google's making. Where Microsoft & Apple are able to provide years of updates to every model of phone their software runs on (with MS literally working with the same vendors as Google), Google has successfully ensured that outside of Nexus devices, updates occur rarely if ever.