Combine two version of app [old and new] in different tech into single app and allow switching to old or new on user choice

hi members,

  1. we have a old version of app build in ionic 2, version 1 live
  2. we are building a new version of same app in react native,

we want to create a app version 2, inside this we want to give flexibility to switch between two version of app [old and new] based on user choice.

our core team is working on solutions but i may take time, any thoughts in this direction will help.