More than 20 years of research has created a large body of ideas, concepts, and theories for model-based development of embedded software-intensive systems. These approaches have been implemented by several tools and successfully applied to various development projects. However, the everyday use of model-based approaches in the automotive and avionic industries is still limited. Most of the time, the engineers work with a predefined set of isolated tools, and therefore adapt their engineering methods and process to the available tools. Today, the industry achieves tool integration by demand-driven, pragmatic, and ad-hoc composed chains of a priori existent commercial tools. Nevertheless, these tool chains are not (and cannot be) seamless, since the integration that can be achieved is not deep enough. This hampers the reuse and refinement of models, which subsequently leads to problems like redundancy, inconsistency, and lack of automation. In the end, these deficiencies decrease both the productivity and quality that could be provided by model-based approaches. To overcome these problems, a deep, coherent, and comprehensive integration of models and tools is required. Such an integration can be achieved by the following three ingredients: 1) a comprehensive modeling theory that serves as a semantic domain for the models, 2) an integrated architectural model that holistically describes the product and process, and 3) a manner to build tools that conform to the modeling theory and allow the authoring of the product model. We show that from a scientific point of view, all ingredients are at our hands to do a substantial step into an integrated process and tool world. Further, we illustrate why such a solution has not been achieved so far, and discuss what is to be done to get a step closer to seamless model-based engineering.