I think this may be more a question of politics and law than history, but I will go ahead and answer the best I can.

Weighing in on the general legal side there is no international law governing the distribution of power between a state and its regional governments, the nature of such a relationship is usually endemic to the country and is typically defined in the countries constitutional, administrative and customary law. As such processes of autonomisation, devolution or decentralisation are not transferable from one state to another as each country has their own distribution of powers and governance, and laws.

Speaking specifically of Romania and its Hungarian minority there has been a long standing fear that autonomy would lead to separatism and possible irredentism too (http://www.nccr-democracy.uzh.ch/publications/bochsl2013wep). Some scholars go deeper and suggest that as a multiethnic country with a history of great border fluctuations, going for autonomy or even federalism would cause national disintegration as it will undermine national identity, the myth of unity and by extension the legitimacy of the central government (History and Myth in Romanian Consciousness By Lucian Boia).