A sparse matrix is a different animal serving a different purpose, i.e., solution of linear systems. Those storage formats are geared for that application: upper diagonal, block diagonal, stripwise, etc.
To be more specific: here tight numerical arrays are presumably discussed. Python and other languages could define an "irregular list of irregular lists" or "aggregation of objects" configuration. Probably Lisp would be better for that. But it is not my driving interest. My interest is packed storage minimizing memory consumption and access time, with bonus points for integration with numerical recipes and element-wise operations.
Again, actual demonstration would be appreciated. I selected an example with minimal deviation from a regular array to simplify things. The shape is essentially a cube with a planar cut across one corner. The Mathematica code shows it is very easy to define in that language. (I am not sure whether it is tightly packed but it shows O(N) performance graphs.)