The M.3 form-factor provides a 30.5 mm surface, allowing manufacturers to add more memory chips, failure capacitors and larger controllers. The M.3 SSDs will thus feature larger capacities, improved speeds and extended security features.
https://www.notebookcheck.net/ADATA-preps-support-for-the-upcoming-M-3-SSD-form-factor-standard.278624.0.html