You have the new paint shader now, this can be pretty much used identically to the heightfield sculpt tool from TG 0.xx.
You'd paint your general shape and plug it into a displacement shader's 'function' input. (Between these two you'd need some sort of small scale fractal shader to add detail to the rounded brush-stroke terrain.) The displacement shader would then go to 'compute terrain'.
Or, If you wanted to export the painted terrain; You'd have to plug the displacement shader into a heightfield generate's 'shader' input(you could use the fractal detail option instead of a power fractal shader for detail here) and then the heightfield can be saved as .ter by right clicking the heightfield generate node.
EDIT: Remember to hit 'generate now' to make the terrain visible. The higher the detail - the longer the generate time but... Here's a little trick I discovered that I like to call 'The Wiggle Method'
When you hit 'generate now', mouse over the little progress window rapidly back and forth with your cursor to accelerate the building process.
