While going through Avengers : AOU quotes In Rotten Tomatoes..I noticed dialogues which refer to a "shadow" and an "angry spider". This is obviously not Black Widow because the character is a "he". So, the only other characters who are spider-related and relevant for the MCU are Jessica Drew and Spiderman. I repeat..Jessica Drew and Spiderman.
SPIDERMAN MIGHT ACTUALLY BE IN AGE OF ULTRON!! Maybe as an easter egg..or a cameo in the end-credits scene. I can be wrong, It may turn out be Spider-woman (Which is still great) or another spider(y) character. I have no idea about the "Shadow" though.(Moon Knight? Black Panther?)