The real dangers of a tornado to homes is lack of a quick dispersion of high pressure inside a home compared to the low pressure inside a tornado.
Without a pressure release valve, homes explode. Secondly the wind can shift homes on their foundation that causes loss of structural integrity.

A safe room only addresses protection from debris, not keeping one's home intact if hit.

Although there is little to be done in a sudden class 5 tornado, I imagine 2 solutions where no cellar is availlable.

1. Build homes with a cental 10 foot square reinforced wind chimney that connects every floor with 5 foot square wind egress channels that connects to the central chimney.

2. Steel anchor cables attached to bedrock or other underground anchors drape the home to wall and roof netting to hold the home stay put and avoid foundation shift.

This a low cost radical idea that comes from my imagination so feel free to ignore it.