I think it is an excellent idea. 18,000ft would be a good choice as it harmonises with the USA and would be good across the whole of Europe if it is adpoted more widely. Mont Blanc is 15,782ft high and without doing the calculations 18,000ft would cover this adequately (can anyone check this).
Having flown worldwide, and extensively in the US, I found that the higher transition level much reduced workload at the more critical phases of flight.