Worst-case execution time (WCET) analysis is indispensable for the successful design and development of systems, which, in addition to their functional constraints, have to satisfy hard real-time constraints. The expressiveness and usability of annotation languages, which are used by algorithms and tools for WCET analysis in order to separate feasible from infeasible program paths, have a crucial impact on the precision and performance of these algorithms and tools. In this paper, we thus propose to complement the WCET tool challenge, which has recently successfully been launched, by a second closely related challenge: the WCET annotation language challenge. We believe that contributions towards mastering this challenge will be essential for the next major step of advancing the field of WCET analysis.