There's some interesting articles being written by a guy on Medium. Called the Gundam NT Design History. Currently only has two articles out, covering the Narrative Gundam and Stein Unit 2.
https://medium.com/@TomAznable/gundam-nt-design-history-narrative-gundam-1b2365c80981
https://medium.com/@TomAznable/gundam-nt-design-history-msn-06s-2-sinanju-stein-unit-2-158d840eaee0
https://medium.com/@TomAznable/gundam-nt-design-history-narrative-gundam-1b2365c80981
https://medium.com/@TomAznable/gundam-nt-design-history-msn-06s-2-sinanju-stein-unit-2-158d840eaee0