There are a lot of innovations out there, but its fairly iterative as the thing that most of us like about these instruments is linked to the tone and style of the best of the vintage period. Things like the use of more stable wood veneers and cleated woods (Dippers), and the use of cast resins or composite materials (Carroll and Kensington) for stability, improvements to the pivot mechanism (Carroll, Edgley) reed design and mounting (Kensington), efficiency in manufacture by utilizing CNC and wire EDM. 3D printing like Jay instruments. The use of high end accordion reeds among all of the hybrid makers. With the light weight and amazingly quick reeds in modern instruments, its hard to find anywhere that improvement is needed, but its interesting to see the minor improvements the best makers make to their instruments over the years.