My question is, how can anyone know what to expect from evolution?
The expectation from evolution is small changes from one generation to the next. Large changes may occur between different generations from the same chain of ancestors over much longer periods of time.
If you don't necessarily know what it "may" come up with how can you be sure it came up with everything we do know exists? If you reason, "because it exists", you commit circularity.
There is no expected goal of evolution. We are not sure that it came up with everything we know exists. But we do know that there's no better explanation so far.
...and they make no predictions for what it will come up with.
Sure they do. They predict that evolution will come up with small changes from one generation to the next - and this is observed in every generation that occurs. They predict that evolution over generations will leave similar looking fossil chains - and this is observed in every fossil that occurs. They predict that DNA will leave traces over past generations and ancestors, and that this chain will match the similar looking fossil chains - and this is observed in every DNA chain and fossil chain we have the information for. They predict that many species will not be able to evolve in time to adapt to a change in their environment and die off - and this is observed for many, many species.
They do not predict that evolution will create something specific (like "a wheel") because that is not how they think evolution works. The changes from evolution may end up creating a wheel. Or they may not. But for anyone to "expect evolution" do just create a wheel - grossly misunderstands how evolution works.
It seems to me a fair apriori prediction would be that we should find a wheel in many species because it's a relatively simple design
What makes you think evolution would create something just because it is a 'relatively simple design?' Evolution is only expected to create "changes." Some will be good, some will be bad, some won't make a difference. Some will be simple, some will be complex.
Think about it, it's a fair prediction to say "earlier" layers should show evolution's trials and errors, but we find the most sophisticated eye design in the Cambrian, for trilobites.
Do you know what even you expect from evolution? Earlier you seemed to expect evolution to provide "simple designs." Here you seem to claim that evolution provided "sophisticated designs."
Regardless of your own confusion - I think it's clear that you do not understand what Scientists expect from evolution.
The basis for saying evolution has the ability to make something is only based on whether that trait exists, it would seem...
Actually, the basis for saying evolution has the ability to "make (anything)" is foolish. Again - evolution doesn't make "things." It just makes "changes."
If the changes help, the changes stay. If the changes don't hurt (enough to kill the creatures before they can reproduce...) the changes stay. If the changes hurt (enough to kill the creatures before they can reproduce...) the changes die off with the creatures and disappear.