Can you play original Xbox games on the Xbox One via backwards compatibility?

Sadly the answer is no. If you take a lot at the different games that are on the original Xbox and then place them against the Xbox One, you will notice a huge difference in graphics and frankly quality. This is because the games on the original Xbox are so different due to different hardware and software's and of course new methods of making games.

The reason the 360 is backwards compatible to the original is because the software isn't that much different, likewise with the 360 to Xbox One, however the original xbox to xbox one is such a large jump that it would cost perhaps a little bit more than what Microsoft want to spend per Xbox that it just isn't profitable to have backwards compatibility on the Xbox One to the Original xbox games.

No. The 360 used software emulation for original Xbox games. So if the xbx1 were to play original Xbox games then it would have to be via software emulation which means that ms will have to write the coding.

Apparently yes. Some games are able to play for early testers. But its unkown if that'll be case when they launch it to the public and if the developers or publishers will agree to let the game be BC.