IMO, all Tesla vehicles (so far) are pretty similar to each other.
On the one hand, Y is a less expensive X.
On the other hand, Y is a bigger 3 with a hatch back.
I'm not an expert in automotive consumer behavior, but I have to imagine that Y will cannibalize some amount of 3 sales. I also don't think that will matter that much - there is so much demand for Tesla vehicles that they are battery limited.