This note formulates some assertions and conjectures concerning an up to now missing case of convergence rates results for variational regularization of nonlinear ill-posed problems in Banach spaces. If the residual term is the $p$-th power of a Banach space norm, then the use of powers $0<p<1$ instead of the common values $1 \le p <\infty$ leads to an artificial limitation of convergence rates. This
effect also occurs for general residual terms when they represent concave monomials of that distance which is bounded by the noise level and expresses some kind of qualification for the regularization method.