It is definitely coming and it will be the full Carplay as Apple won't let BMW cripple down their service. It will work as an overlay similar to the iPod-out and will probably only be available in combination with BMW's own NAVPro. Don't count on it to have Carplay as an iDrive alternative for media/satnav^^.
Sources say it should be out in 2016-2017. I presume that the 7series will get it first by the end of this year and it will roll out down the other models as the new touchscreen-idrive will be added to those (tbn that a touchscreen is required to operate carplay).
So as for the 1/2 series, it should be available as an option by 2017/2018...