Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update 2014?2019
Note: Common Core State Standards mandate teaching handwriting skills before and during grade 1, while not mandating it later
Handwriting in the 21st Century Summary of Research.
Greater letter-recognition skills in children after three weeks handwriting practice versus typing practice
"The influence of writing practice on letter recognition in preschool children."
I'm pretty sure its linked to greater cognitive skills in other ways too.
This however is not prove it should be taught more, at best its one factor.
One reason is in the future speech recognition technology or gesture reading or brain reading technology may replace typing.
Berninger, Virginia. "The Neural Correlates of Handwriting and Its Affect on Reading Acquisition"
Handwriting is associated with greater cognitive activation and development than typing
Handwriting information may lead to greater understanding than typing, as note-taking was found to be more beneficial when handwritten
Pam Mueller and Daniel Oppenheimer. "The Pen Is Mightier Than the Keyboard."
Multiple, critical brain regions activated by free-hand writing
Arif, Ahmed. Analysis of Text Entry Performance Metrics.
James, Karen and Laura Engelhardt. The effects of handwriting experience on functional brain development in pre-literate children.