This is a great idea and an excellent mod, thanks a lot. My kids and me use this mod since 0.4.13 and we truly enjoy the effects. The changes to the environment are smoothly taking effect and the overall appearance is very appropriate.
Maybe you could extend some of the effects to new default nodes like e.g. default:cobble_microslab and alike?
Example: The microslab could take cracks (maybe difficult) or could just vanish (more easy) like cobble can degrade to gravel already.
In our LAN world we are building bridges with cobble/desert cobble and we use both cobble and cobble microslabs for streets and the latter as a cover for smooth cobble stairways for streets rising into the terrain. Naturally a microslab cannot change into gravel as this would produce an unwanted block node instead of a surface node.
Some of my kids love the need of regular repairs to our streets. Your mod adds positively to the game feeling.