There are two women I will occasionally call "mom" but it's in a very lighthearted, joking way - like "aw thanks Mom!" if they give me dinner, etc. One is my mom's friend of 25+ years who really is like a second mom to me - I've grown up with her, spent a ton of time at her house and her son is my age and we were best friends growing up. The other was my mom's friend, we were super close for probably 8ish years, I used to stay at her house for 7-10 days at a time in the summer, we'd go to horse shows together. All the barn girls in our little group called her mom, but the others a little more freely than me.
To say it seriously though, I don't think I could do it. I don't think it's wrong or abnormal but it would just feel way too weird for me. Perhaps it wouldn't if my mom had never been in my life or anything, but we are so close and always have been that I would find it very strange to call another woman "Mom" in a serious, emotional way.