When was the last time Swedish had different conjugational patterns for the word to be and when did är take over the whole 1,2,3 person singular. I don't know if Norwegian, Danish and Icelandic
have the same occurence.
It's interesting to know when this happened. It's actually not that weird of a phenomenon. We have Luwian with the same issues, then French has the problem where plural forms sound
the same and can only be distinguished with writing and than we have AAVE where we have I is, you is and he is.