We've been provided with some of the leaked documents from the "Sony Hack", and they offer up more details on the deal which was being discussed between Marvel Studios and Sony Pictures in regards to the future of Spider-Man. It's worth noting that some of this contradicts and confirms what we heard from some of those obscure foreign sites (who probably made up that information for attention and "via" traffic, especially as most of it sounded like glorified fan-fiction).
If Spider-Man appears in Captain America: Civil War, Sony will co-finance 25% of the movie. Marvel then co-finances 25% of Spider-Man's next solo film which is scheduled to be released in July 2017. The deal allows Sony to use TWO major Marvel characters and continue the plot from Civil War in regards to how it relates to Spider-Man. Spider-Man would also appear in Avengers: Infinity War - Part 1 in 2018, with another Marvel produced Spider-Man movie following in July 2019.
Sony asked for approval over the costume, script (but only the parts specifically involving Spider-Man), and casting, with said actor required to sign a three-picture deal or more. The way this part of the document is worded makes it sound very much like a collaboration rather than one studio having more control than the other. They do however point out that Kevin Feige must serve as a producer, and if for some reason he leaves Marvel, they would be allowed to select his replacement. They also want Avi Arad and Matt Tolmach to be given executive producer credits, and state that it would be pre-agreed that Drew Goddard both writes and directs the first movie.
We've also seen documents which indicate that The Amazing Spider-Man 2 earned only $65 million BEFORE overheads, and that they expect earnings to significantly increase after making the deal with Marvel. These are internal documents, and it's not clear how much would change as the deal is discussed. However, this appears to have been put together following discussions rather than as a proposal. We have of course heard that talks broke down, but nothing specific in regards to why, and various outlets have since reported that this is going to happen. Stay tuned for updates...
On the business side of things, if any of the Marvel movies Spider-Man is included in misses their release date, Sony would be paid damages of $100 million, and the deal would be terminated. Sony have only three years and nine months to start pre-production before the rights revert, and Captain America: Civil War would reset the clock on this period. Sony also asked for Marvel's help in ensuring that the "D Machine" would have to be accessible for Spider-Man's solo movies in regards to their TV channels, radio networks, theme parks, and more. The deal would be announced at a press event by both studios on a mutually agreed upon date.