It is really all pointless as there are as many UK citizens residing in the EU as there are EU citizens residing in the UK.
So they cannot be used as a bargaining chip, given that the EU has exactly the same bargaining chip. They cancel each other out.
It is just more anti EU propaganda to soften people towards a hard Brexit, portraying the many EU citizens living, working and raising families here as a drain on our resources, people we would be better off without.
The reality is the majority contribute to the UK, and if we are forced to swap them for the mainly retired residents of the UK who live overseas, we will be worse off.