Systems, devices, and methods for detaching an implantable device from a delivery system are disclosed herein. One aspect of the present technology, for example, is directed toward an elongated shaft having an inner surface that defines a lumen that extends distally from the proximal portion to an opening at a distal terminus of a distal portion. In some embodiments the distal portion includes an inner polymer structure having a first portion and a second portion positioned distal of the first portion along the length of the inner polymer structure. The first portion can have a first stiffness and the second portion can have a second stiffness less than the first stiffness. The distal portion can further include an outer polymer structure disposed around the inner polymer structure and a coil wound around the inner polymer structure and disposed within the outer polymer structure.
