The current EU citizenship is supplementary to national citizenship from an EU member. This is written in the Treaty on the Functioning of the European Union, and was first agreed on the Maastricht Treaty (1992).
WHAT IS EU CITIZENSHIP?
Anyone who is a national of an EU country is automatically an EU
citizen. The principle is enshrined in the EU's treaties and is a key
factor in developing a European identity. EU citizenship does not
replace national citizenship. It is additional to it and gives people
The EU, being a difficult to define mixture of federation, confederation, and international organization, does not have the central power to, alone, define the major status for EU citizenship. This would almost certainly require a new treaty and/or consensus from all members. Even Charles Goerens that proposed an ammendment (882) to the EU regarding non-EU memmber citizens EU citizenship (so similar to the notion advanced by this citizen initiative), admitted the difficulty of implementation to EURACTIV:
The proposal would need all 27 governments and parliaments of the the
EU to agree to treaty change. Do you see any chance of that happening?
I know that unanimity is a tough ask. But the idea should at least be
discussed. The proposal is out there and you see the response it has
gathered: it is substantial. Never in my political life have I seen
people so enthusiastic about something or received so many emails of
support; it verges on madness. We have for the first time stumbled
upon an enthusiastic commitment to European achievements. What we are
seeing in the British Isles as a result of this proposal has not been
seen in the other member states. I think it would be foolhardy to not
act on it.
Given this assumption it is extremely unlikely that this citizen initiative (which curiously is a new EU citizens right introduced in the Treaty of Lisbon) will ever come to fruition. The reasons are that there are many member states that would outright vote against (ergo veto) this proposal. In fact I would argue that any member state dealing with significant separatist movements (UK, Spain, Belgium, Germany, etc.) would likely veto this.
The process through which a citizen looses its citizenship is named denaturalization:
Denaturalization is the reverse of naturalization, when a state
deprives one of its citizens of his or her citizenship. From the point
of view of the individual, denaturalization means revocation or loss
of citizenship. Denaturalization can be based on various legal
In some countries this is possible even for citizens born in it (UK and Canada for example). However notice that this is considered extreme and there are several international agreements that preclude the loss of citizenship with the acquisition of another. This is so as to avoid the condition of stateless.
Given the dual nature of EU citizenship (supplementary only to a member nationality) this principle is being followed in the process of denaturalization. For this reason I don't think there is a legal basis to support this initiative even if submitted to the European courts of justice.
Notice that I'm not saying that is not possible and I must admit I find the notion appealing. Nevertheless I think it would be unrealistic to expect this to happen in any foreseeable future.