Just seen this on FMP:
https://www.findmypast.co.uk/worldtree
They say this:
Millions of people around the world are collaborating to combine their family trees into one, single, global family tree.
Private Findmypast family trees are not included in our new global family tree searches
Our common goal: To spend less time searching for ancestors and more time discovering and connecting.
Surely the problem is going to be "garbage in, garbage out" as people will be adding poorly-researched trees which are wrong, just like with every other similar project which has been tried before.