Well #Im2SMS an app designed to import #whatsapp messages into your phones internal sms storage system is now in beta. It supports previewing both group and 1:1 chats and importing 1:1 chats including media such as photos or videos.

You can become a tester here. https://play.google.com/apps/testing/com.goldmaster.im2sms?pli=1

To cover play store costs, the app is 59p but you should be able to download for free.