While future Immigration requirements cannot be predicted, there are some actions that Companies and individuals should consider right away.
Undertake an audit of EU Nationals working in your company. As there is no UK requirement for these individuals to register with the authorities there is no central register. You will at least have identified who they are, and you will be able to update your records going forward. It is suggested that you should also record the date of any EU National joining your company. However the employee may have worked in the UK before joining you.
It would also be helpful to create a schedule of absences to prove that they have not been outside of the UK for 180 days or more in every 12 month period for the duration of their stay. This is needed to ensure the individual can confirm that they have maintained their continuous residence in the UK.
This situation is slightly less complicated in that it is a requirement in most other EU countries that Employees and families have to register with the Authorities for any stay that exceeds 90 days. However it is recommended that an audit is undertaken so that you are prepared for any changes post Brexit.
Each country has individual rules and requirements and it is recommended that individuals explore the options open to them and their families and decide the best course of action to protect them from future changes. It is important to note that some countries do not recognise Dual Citizenship.