>and it's broken. one of the dependencies symengine uses some kind of is_windows check https://github.com/symengine/SymEngine.jl/pull/150

What do you mean it's broken? Is it because SymEngine couldn't install? SymEngine seems to have a lot of issues because it relies on Conda and builds its dependencies in an odd way. Python package management is notoriously rough, which is why we are excising it from DiffEq v6.0 (https://github.com/JuliaDiffEq/DifferentialEquations.jl/issu...).