Photos.app no longer detecting SD cards for import
In the Terminal.app, is your SD card appearing with this command ? 

ls /Volumes 

If not, the problem is that your SD card is not mounted.
https://superuser.com/questions/256445/macbook-pro-not-detecting-sd-card
https://discussions.apple.com/thread/5349557?tstart=0

If your SD card is mounted, you can import your photos without the dedicated tab :

in the menubar 


  file -> import


keyboard shortcut 


  CMD + Shift + I