I assume once they start producing the v1.5, they will stop making the v1.1, just like when they went from v1.0 to v1.1.
W360 has mentioned in the past that v1.5 would be simpler to manufacture, because the original design for the T1 was supposed to only be used to make 200 cases only, and then never made again, therefore the case was never refined to be produced at scale. By simplifying the design in ways that keep the functionality of the case the same, but reducing the complexity for the machines making them, you can reduce the cost of the case. This is what I assume is happening to make the case cost less now (an example being that the front panel is now one piece instead of two, which cuts down on potential defects and is easier to make)