Soft Brick? I closed the magnetic case cover of my Nexus 7 while my newly flashed Rom was optimizing apps and....Brick
Since you do have working fastboot access, you have a few options from there:

You can...


Get a custom recovery like TWRP. Then run fastboot flash recovery /path/to/twrp.img.

With TWRP, you can to try to reinstall ROMS, do factory resets, and make backups of your current system (Which may be a good idea, even if it's bricked).

Do a factory reset with fastboot format data and fastboot format cache. 
Try to install stock Android (keeping data) from the Factory Images by running included flash-base.sh, included in the image download. 
If all else fails, you can unbrick it by running the flash-all.sh - which will essentially reset it to a like-new state, with the stock OS and no data.


If you wind up doing a factory reset after all, you can use Titanium Backup to extract the apps and settings from the TWRP backups.