How effective are the efforts to control the spread of arms (including biological and chemical), especially nuclear weapons, likely to be in the future?
It is, of course, hard to know how effective these measures will be. However, it is likely that the efforts will not be effective.
It is true that many countries will not try to get nuclear weapons or other weapons of mass destruction. However, it is often the case that those countries will not try to get WMD simply because they do not see the need. There are many countries, such as Germany or Switzerland, who do not think they need the weapons. They believe that no countries will attack them or that other countries will protect them in the case of attack. If this is true, there is no reason for them to seek WMD.
However, countries who think that WMD will be useful to them are not likely to refrain simply because WMD are illegal. We can see this from the case of North Korea. They simply chose to withdraw from the treaty and are not getting WMD. This shows that countries will not necessarily abide by the provisions of the treaty if they do not feel it is in their interests.