Good point, and yes you are right, the depth of the HD path matters. We are currently trying to get feedback from HW dev to understand their limitations with respect to this.
However it seems the computational complexity is linear with the depth of the HD tree.
Also there are other ways to reduce the depth of the EIP1775 path, such as only using 128bits Uids.
In any case, that’s a good point and I’ll report here the results of discussions with HW devs.
Edit: Just talked to Ledger CTO we will do a benchmark (time / depth) analysis and report the findings.