The Newton improvements might be in the works. First, in Waltham at the Woerd Ave trail end, there's a low stress road connection to the Auburndale Park Path in Newton, going to Comm Ave.

From there, there's a series of projects in the works in the planning stages at least, though, hurry up and wait...

https://www.solomonfoundation.org/projects/riverside-greenway/

I know pedestrian improvements crossing Comm were recently funded by Newton/MA for starters, and one of the next steps, the rebuild of the pedestrian Boathouse bridge over the Charles, is funded by MA for construction in the next few years.