Mag world view: Guardian going tab?; PM cover girl; apps' uneven growth; paper real "killer app"

• Guardian considering move to tabloid format and out-sourcing of printing to rival publisher (Press Gazette) 
• App usage still growing, but unevenly (FIPP)
• Why paper is the real "killer app" (BBC)
• Theresa May to become first PM on the cover of American Vogue (Guardian)