I don't play the java version anymore so I can't personally confirm it, but there's nothing in the wiki that says they were "phased out". I guess they're still there, therefore should eventually be added to Win10/PE.
I think the problem is that you can't really control it. Stick a piece of coal in it and it runs for about 3 minutes- on a flat surface. It can't push another minecart up hill. You can't ride in it- your weight makes it stop. Interesting to watch... for about 10 seconds..... sorta like the model train circling under a Christmas tree.