ROBOTIS and Open Robotics will ensure that pre-order users do not inconvenience the delivery and use of Intel Joule. Currently, we have a substantial number of Intel Joule Boards for TurtleBot3 Waffle, so we have no problem with customer support.
I'd like to ask about what you will use after Joule, but I'm guessing that this news is as much of a surprise to Robotis as it is to the rest of us and you haven't had a chance to evaluate alternatives yet.
I would like to take this chance, however, to ask for an option to purchase either Turtlebot 3 model without sensors and a Rasberry Pi or Joule board. Some of us have those, or suitable replacements, already.
As you said, we are also looking for Joule's next board. We are discussing this with Open Robotics and partners, and we plan to announce related plans in the near future.
Also, shipment of preordered TurtleBot3 (Burger, Waffle) will start next week. In addition, the TurtleBot3 package, excluding the SBC and sensors you mentioned, is scheduled to be sold from the second half of 2017.
Another interesting SBC is the UDOO x86. It has an Intel quad-core 64-bit processor, plus an onboard Arduino-like processor. I believe that it will take Arduino shields and is programmed with a similar IDE. I haven't had time to set mine up yet, but it's supposed to run Ubuntu out of the box.