What are the origins of segwit? Was it long proposed as a nice idea by multiple people or did it arrive out of nowhere from a single source and tickle everyone pink?
SegWit was presented by Blockstream's Pieter Wuille to the world at the end of the second Bitcoin Stalling conference in Hong Kong. The video of his talk should be on YouTube. Apparently it was a surprise to most people there, except Blockstream folks of course. Indeed I would say that Blockstream planned the conferences to be just a stage for the SegWit announcement.
According to Pieter himself, he thought of SegWit some time ago, but put it aside because he believed that it would require a hard fork. But then Luke Dash Jr. found a way to make SegWit into a soft-fork type of change, by using a script hack and redefining one of the NOP opcodes. That made it possible to deploy it in Blockstream's favorite "stealth mode". (That is, the change is effective as soon as a miner majority adopts it, whether full nodes, users, and businesses like it or not.)
AFAIK, the only significant improvement that SegWit brings is to fix various malleability problems in one go. Even that benefit could be obtained much more cleanly by other means, without changing the block and transaction format; but this cleaner solution would require a hard fork, and also the discarding of Pieter and Luke's ingenious hack -- so obviously it could not happen.
I haven't heard of the "fraud proofs" in a while. In the initial description, they seemed to be more "hints" than "proofs"; and it was never clear how they would be used, and for what.
One interesting "benefit" of SegWit was to make people aware that soft forks are actually more dangerous than hard forks. With SegWit's "extension record" trick, a soft fork can achieve many of the taboo changes that were thought to require a hard fork; such as increasing the block reward (and therefore the 21 million issuance cap) or confiscating coins. As soft forks, those changes would require only the agreement of a mining majority, without the consent of the rest of the community. However, for that same reason, there is nothing that the community or the developers can do to prevent non-consensual soft forks.