Although development practices for apps have matured, cross-platform development remains a prominent topic. Typically, apps should always support both Android and iOS devices. They ought to run smoothly on various hardware, and be compatible with a host of platform versions. Additionally, device categories beyond smartphone and tablets have emerged, which makes multi-platform support even trickier. Truly developing an app once and serving the multitude of possible targets remains an issue despite having crossplatform frameworks that are acknowledged by practice and research. The technology unifier remains to be found, but Progressive Web Apps (PWA) might be a step towards it. In this paper, we analyse the foundations of PWAs in cross-platform development and scrutinize the status quo of current possibilities. Based on our observations, we investigate unified development, and discuss open questions. We seek to stimulate interest and narrow the immense gap that has arisen since industry started to embrace PWAs.