Lots of optimization passes, even, are relatively obvious (not necessarily trivial, but they make sense) - to my eye at least, the Voodoo magic is in the scheduling and code generation
Yes, for the code generation one needs to well understand semantics of the target language. And when it's a low-level language (Assembly), the "voodoo magic" mainly relates to generic understanding of the lower-level architectures. However, there might be compilation to another high-level language (in case of a transpiler), and by itself code generation at this stage is not that hard, simply because a target language is more understood in this case.
Instruction selection topic, and where to place the data -- on the stack, or into registers (and how a register allocator works) also mainly relates to the lower-level.
> until you get into the backend
Yes, and that's why I think it should be a separate class, specifically for higher-level compilation, and a low-level compilation.
We'll be covering this in "Essentials of Compilation".
And if you want to just generate byetecode doesn't Truffle on Java do that far better than DLR? Truffle seemed to actually achieve what DLR promised but never really managed - genuine support for dynamic languages on .NET/JVM.