Would it be useful as new stage in diplomacy that legions if they wanted to merge with one another. Yes it might be a bit tricky to put into action but it would clean up some current legion issues for instance, leaders who wish get rid of a legion with a lvl 4 base or higher can and move to another.

In theory the way it could work is that the legion who is looking for merges can send invites as they do with trade and battle packs. The legion which receives the invite before accepting will be able to view the legion and what they are offering in terms of a legions base lvl, what they produce, member numbers, CT Lab discoveries and other details.

Once a legion accepts then the legion is then disbanded distributing the base funds into the legion in which they have merged with and all the members will automatically be in the new legion. Naturally the normal legion size is 50 so this would only work if there is enough space for members which would be of great use to smaller legions which may be struggling to gain members.