The example of Acorn and Pixelmator is strange. Acorn is not much easier to pick up, it has almost all the buttons. Personally found it harder to use and understand what it's for. If you don't understand it's particular use case and want to do a common task that it doesn't have, it suddenly becomes very hard to use.
In the current app ecosystem pro and consumer apps are indeed divided but there's no reason for this except tradition. You can present a full featured app as a simple consumer app by changing its UI. Then slowly reveal buttons and features if you detect it gets used everyday for example.
You could use a feature search UI, letting people use keywords to find the features they need. Basically a modern skin on the old command line.
Just because apps are done a certain way now doesn't mean you should copy this trend.
Programming languages are a good comparison. A full featured programming language can be easy enough for beginners if it has good tutorials and obviously serve serious users. A limited programming language will become hard in many beginner cases. DSLs usually make it clear what they are, a GUI like Acorn doesn't.
It's possible to make full featured programming languages look easy to beginners. LISP does it in a way, although its syntax looks unpleasant the fundamentals are easy to pick up. The same can be done for GUIs by introducing fundamentals that repeat. That might seem hard because today we have a mishmash of menus and buttons, where the only way to simplify is to have fewer buttons and menus and make them bigger.