Is there any other country which might have the ability or credentials to become a permanent member of the UN Security Council?
Apparently, not; at least, it would require amendment of the Charter of the UN:
Current edition of Article 23 of UN Charter says:
- […] The Republic of China, France, the Union of Soviet Socialist Republics, the United Kingdom of Great Britain and Northern Ireland, and the United States of America shall be permanent members of the Security Council. The General Assembly shall elect ten other Members of the United Nations to be non-permanent members of the Security Council […]
It has been several times suggested the addition of new permanent members.
There were also several suggestions regarding increasing the number of non-permanent seats and also "semi-permanent" members (those whose rights are somewhere in between permanent and non-permanent).
At the moment, no proposals have been accepted yet:
Any reform of the Security Council would require the agreement of at least two-thirds of UN member states, and that of all the permanent members of the UNSC enjoying the veto right. — Wikipedia, Reform of the UNSC