I used to be big fan of using Makefile for web development, but have since changed my mind, because make is not very good fit for watch-mode incremental building.

The data model of makefiles is perfect for watching and rebuilding. All you need to add is something that monitors the source files for any changes and runs 'make'.

That sounds like a great idea. Does anything like that exist already?

Easy enough (assuming $SRC is your list of source files and 'all' is top level target) 'make watch' could do this

   watch:
        while ! inotifywait -e modify $(SRC) ; do time -p make all; done

https://github.com/emcrisostomo/fswatch