Here is a good post on this forum about exchanging ground and neutral wire. It’s not safe to do so.
As for why electricians don’t bring neutral to the switch box. Well, it was not a requirement just like wire colors and sometime that’s the most feasible and cheapest way. Also there is no such thing as smart switch that required neutral back then. You can thank the many standards between not just states but cities as well.
I know it’s too late but do check your wiring first before the purchase. Hopefully you can still return the Wemo switch or use it somewhere else.