I don't know about desktop. I just use my phone/ipad for 90% of my email, so that works fine by me.
As for being hired, Readdle makes a ton of ios apps, and are profitable in their own right. Also, while Spark is free, some of the features they've hinted to as coming in the future will likely be in-app purchases / upgrades, that will allow it to be profitable as well.
Do you know if they're going to do a desktop version too?
(Or, to be more pessimistic: "How long until that gets acquihired and killed off too?")