Not sure why this is needed. You would change the code pattern from:

to

It's no shorter, clearer, or cheaper. The second line has a hidden SO3 constructor and like the first option leaves an object to be garbage collected. It also makes the check for matrix validity happen, which is in principle a good thing, but is expensive. If an SMTB module knows that the matrix belongs to SO(3) then that check can be circumvented by

This is a "feature" user's can also use but at their own peril. In your interpolator you know that the matrix you compute is in SO(3).

Given the usefulness of the functionality, and their independence from the rest of the code, nothing in SMTB depends on these, the risk is low, and should be added. But see comments below.

These are a really useful addition. The control poses

are passed as a list of SE3s not as a multi-element SE3. What's the thinking there?

There are multiple interpolator classes, each algorithm specific. Would it be better to have one interpolator class with a passed argument to say which one is used. This is kind of the approach that SciPy takes with optimisers and integrators that have a method parameter. Simplest approach would be a wrapper class that instantiates one of the specific classes, all of them with a common parent class.