The process of the next constitutional reform of the European Union (EU), of which the publication of the report of the German–French working group (2023), as well as the adoption by the European Parliament of the proposal to amend the EU’s treaty basis in November 2023, was an important milestone, as announced by the old-new President of the European Commission, U. von der Leyen will be continued. The directions of this reform indicated in multiple EU documents, including also the current practice of applying EU law, call for an in-depth reflection on the present status of medium and small-sized Member States from Central Europe and the consequences of the proposed solutions for them. Having in mind the title of the volume “The European Union 2004–2024: Twenty Years of Legal Experience, Challenges and Growth after Unprecedented EU Enlargement”, the chapter will be definitely focused on experiences and challenges from the perspective of Member States which acceded to the EU respectively in 2004, 2007 and 2013, and which belong to small and medium-sized countries and are located in Central Europe. The overall assessment of 20 years of membership is positive, although the process of integration of these countries has been completed neither at the economic level, reaching 51% of the EU average real GDP, nor at the institutional level, i.e. the omission of representatives of these countries from key positions in the EU. The proposed avenues of economic development for the EU as a whole, as well as the proposed constitutional reform put forward by the Commission, the European Parliament, as well as the largest EU states, may widen the persisting gap between Central and Western Europe. However, without the elimination of this imbalance, an economic leap for the EU as a whole, its resilience, including against military threats, and further enlargement are out of the question.