I guess it would require all eurozone members to agree on the project with the same terms and without conditions. I'm not expecting that anytime soon.
My understanding was that the ECB could pass down decision based on "consensus" or "majority" rulings, rather than requiring complete agreement from all its members, but I'm not from Europe so someone can correct me if I'm wrong.
But having said that, I find it somewhat surprising that even developing/underdeveloped countries are actually weighing up the possibilities of launching their own CBDC in reaction to Bitcoin
I doubt developing countries are considering a CBDC in an effort to stop bitcoin. Rather, they are being forced to consider it due to developed countries considering it. There are lots of developing nations which already use USD or some other major currency as a surrogate for their own currency, due to inflation, counterfeiting, easier trade, wider acceptance, etc. Should we end up with a digital dollar, then it would likely become incredibly easy for citizens of these countries to use it for all purposes, rending the country's own currency less valuable and pushing the country towards dollarization, which is something that the government may not want.