Unfortunately there will be almost no compatibility between 1.X and 2.X. 2.X will be based on DAZ Genesis 8 as a starting point (1.X is Genesis 2), and the rig (joints) and skin mesh/UV/textures are all different. In addition Genesis 2 clothing won't generally fit Genesis 8 figures due to change in rest pose and minor changes to base figure dimensions. Some sim hair might be able to port with tweaks to the scalps, but I'm also looking to improve this so can't yet guarantee compatibility.
I'm also upgrading from very old Unity 2018.1 in 1.X to Unity 2020+ in 2.X and moving to a completely new rendering and materials system. This will bring much better looking and more capable graphics, but at the cost that existing materials in 1.X won't have a direct migration path.
I'm using a similar params system in 2.X, but with improvements for animation, undo/redo support, and a different UI hookup system. Param names, uids, and parents are also going to be completely reorganized to make more logical sense and will be getting a search and filter system.
The 2.X animation system is being redone as well. Mocap via trackers will still be supported, but the underlying engine will be different to support tracks, patterns, editing, and improved storage (faster save/load).
Plugins will be getting a proper API, and any of the the existing plugins that are digging deep into VaM code will likely not port easily.
This probably all sounds like bad news, but my feeling it is time to break free of 1.X chains and fix a lot of the core issues and also leap into more modern technologies (Unity HDRP and DOTS). That requires breaking backwards compatibility.