Of the approximately 2700 people in my family tree about 50% are deceased and 50% are alive but of those that are alive I would say that I know and have the contact details of not many more than 20 people and up until recently they were all in my immediate family. Part of my interest in family history is to try and make connections to my family diaspora wherever in the world they may be. The strength of Wikitree, from my personal point of view, and the reason I have been posting my tree on this site, is that because the names are directly searchable on Google, I have been much more successful in making the connections than with other sites such as Ancestry. So far I have discovered 'cousins' in Australia, New Zealand, USA, South Africa, Canada and England through Wikitree and they have been through direct contact by email rather than using a proprietary messaging system which is an advantage. When I make a connection I do share any information I have on their family, encouraging them to correct, add to and generally enhance it. I find they are mostly interested in the extensive ancestral information I have researched. I offer to put them on the Trusted List for their family members but despite encouragement I have yet to persuade them to add information of their own. Some have sent me additional information by email which I have then added myself. One added a photograph of herself. And if they wanted their profile removed I would totally understand and ensure that this happened or if they wanted to manage their own profile I wouldn't stand in their way - it was just that I wasn't told that this would happen when I added their email address that took me by surprise.
Sorry for this ramble but it was just to explain that your (understandable) suggestion just wouldn't work for me in most of my family tree. You could almost say that I'm coming at things from the opposite direction - rather than consult with my living relatives before posting the information, I'm using the information that I have as a 'hook' to make connections (while working within Wikitree's privacy framework). As an example two of my recent Wikitree-facilitated connections have resulted in an emotional reconnection with their family one generation on when emigration had resulted in a family disconnect for those that emigrated.