There won't be a Spider-man cameo in The Avengers. Why do you think Sony moved so fast on rebooting the franchise, so they retain the rights to the character. They sure as hell aren't going to "loan" him out to Marvel/Disney. Same with the X-Men, X3 and Wolverine were both rushed through production so Fox could keep the rights.
Why move fast on the reboot? I'm seeing it being their must lucrative property - one that brings in a lot of money. Why reboot it "fast"? The third one for the vast majority of the population thought it sucked. Thus rebooting it rather than a sequel. Also is it fast? I don't think so, it's the same amount of time between other Spidey films if not
longer. Also I have no idea how you can compare it with Fox's decisions - Fox at
that time was run by a moron and thus every film that came out
under that guy? Was a failure and piece of ****. That's why X-Men: First Class was a surprise hit - it showed an obvious change in management somewhere within the company chain. Sony is not Fox.
Having worked in the industry, believe me when I say - there is no competition between them. At box office? Yes. In the working environment? No. They lend out sets, studios, and costumes to each other all the time. They collaborate creatively on films all the time. Some films, although rare, have about three major studios behind them. THREE. I don't see why it would be any different here. They both have a lot to gain - especially Sony since it would give more awareness to the Spider-Man reboot. Plus tying it in in some way would be a smart business solution - it's the surest way to draw attention.
As said, Fox is - well at that time? Fox is Fox. Fox was run by an idiot. Sony never has been. And despite what people want to think, the studio "competition" is only in the audience's head and when it comes to box office. I'm IN the industry. This is 101, first day, material WITHIN a big major studio with ties to these kinds of properties. And looking at it from a box office stand-point, both would stand to benefit. I'm not saying Spidey is guaranteed, but what I am saying is it is possible that they've agreed on some arrangement that would be beneficial to both parties involved. They both stand to gain more audience members and awareness from it.
As to merchandising, as already pointed out, acquired by Disney. Thus it's down to film politics now - in which film politics? We work together.
Once again, not saying it will happen. Just business wise? It would be a wise decision on both parts to firmly establish MARVEL this summer. There's a lot of competition, despite being big properties, especially from DC. TDKR probably looks like a giant right now.
This would give them a leg up.