as i saw GDC the Work Graph is rely on mesh shader and there is a minor difference in implementation of mesh shader in RDNA2 (Rx6000) vs RDNA3(Rx7000) so i think it is possible to support rx6000 series with little to no cost
it seems its not rely on mesh shader and it isnt required for "D3D12_WORK_GRAPHS_TIER_1_0" feature set and it require mesh shader for "D3D12_WORK_GRAPHS_TIER_1_1" so it might be possible to support older cards