One question in my mind is whether the linear nature of the interp() function will change how the change point works. I.e., the model parameters are a linear combination over the probabilities of the change point, but the discretized version of the model uses a simplex of probabilities for each discrete time point. The softmax function is highly non-linear, so it might allow for more discontinuous change breaks, whereas this version might allow for smoother change breaks as the weights evolve.
Obviously something that could be tested with simulations.