Good point! I think you're right.
So currently there are two narrowly defined options for career progression:
* technical leadership on core project/domain
* engineering management
Perhaps instead of eliminating the depth option for the technical track and making the T shaped depth/breath mandatory, just make it an additional option to provide an additional track for people to take for career progression.
* deep technical leadership on core project/domain
* broad-based technical leadership on core project/domain and supporting role on multiple projects
* engineering management