Wildcards have to be dealt with carefully.
I think the idea of a challenger series leading up to a slam is a fantastic idea. In fact, I would be almost 100% in favor of it.
However, there is one minor problem that I see... mainly for people ranked 90-110 who are constantly on the threshold of earning main draw spots at majors. Some of these people may opt to spend their weeks trying to qualify for smaller ATP tournaments. I think that if this series idea is done, it should include ATP 250 events as well. By the time the slam entry lists are finalized, the person who did not make the main draw with the highest amount of points from challengers and 250 events gets a wildcard (or top 2 or 3).
I am also very much in favor of having challenger winners gain a wildcard into ATP events. But there is also a very small issue with this:
1. Where do we draw the line? Surely it's more rewarding to win Shanghai CH and get WC to Shanghai Masters (just the example used) as opposed to winning CH in March and getting WC to Estoril open. In order for this to work, players would have to request/claim their WC during a tournament that runs EXACTLY 2 weeks after the CH that they won.
2. What if there are 4 challengers one week, and only one touranment 2 weeks later (let's just say Winston Salem since it's the only tournament that week). Do 4 people get WC??