The __numpy_ufunc__ mechanism likely is easily extended to all relevant numpy.core.multiarray functions. This would also enable several pure-Python Numpy functions (e.g. hstack, vstack, ...) to work transparently with 3rd party classes --- as long as array/asarray are not called, things should work out transparently.

It might also make sense to add a helper function to multiarraymodule so that the override mechanism can be invoked from Python side. This could be a sensible alternative e.g. in the case of linear algebra functions.