Throughout the years, the attention on technical debt experienced a steady growth, and can now boast to be a consolidated concept within the software engineering field. Despite the growing academic and industrial interest in the topic, a category of technical debt appears to date to be unexplored. In this new idea paper, we introduce the concept of turnover technical debt, i.e., technical debt that arises when developers leave projects with software artifacts other developers will struggle to work with. Our contribution presents an initial formulation of the phenomenon, which intuitively revolves around two co-occurring properties in software artifacts, namely (i) centralized ownership and (ii) low understandability and suboptimal documentation. Based on these two properties, we present an approach outlining a conceptual basis to quantitatively observe turnover technical debt via a mix of repository mining and static analysis. We complement our contribution with a small mix-method case study conducted with the twofold goal of assessing the viability of the proposed measurement approach and collecting initial insights from practitioners on the phenomenon. The gathered results point to the relevance of turnover technical debt in practice, and to promising avenues to more precisely measure the phenomenon.