There are many reasons for the delay, one of which is Elon Time™, but the previously mentioned improvements to F9 and being able to launch many payloads with it

There are many reasons for the delay, one of which is Elon Time™, but the previously mentioned improvements to F9 and being able to launch many payloads with it instead is also among them. As to when it will fly, I expect by the end of the year. They have finally begun static firing actual rocket cores recently, including the heavily redesigned (and another reason for delays) center core.