Long story short: YouTube is capricious and prone to unexpected breakage due to automated copyright strikes. Vimeo is a terrible option unless you pay to unlock their "Pro" featureset.
By contrast, the Internet Archive is a non-profit organization which describes itself as 'an American digital library with the stated mission of "universal access to all knowledge."'
Due to their non-profit status, they operate a much more user-friendly service, especially for media archival efforts like this.
The site is far less likely to have copyright issues, as there are no robots on the site (as far as I'm aware) so a rightsholder would have to go to a piece of media's page and issue a takedown on it. Generally copyright isn't policed on promotional materials like trailers, so it seems likely to me that this site could prove useful as a long term repository for movie trailers.
A way to make such a resource a lot more user-friendly would be to integrate TMDB with Archive.org by allowing Archive.org to act as a source for media files.
"Are you just some crazy user from the internet? How do we know this is kosher?"
Per their statement here: http://blog.archive.org/developers/
"Internet Archive encourages developers to add media to archive.org as well as to consume and repurpose metadata and media."
It seems like you guys would be a match made in Heaven :)
That link also provides detailed information on the simple process of accessing stuff stored on the Archive.
I want to help contribute but theatrical trailers deserve to be seen in high definition, so Vimeo just isn't great for me.
I also would very much like to ensure these files are readily accessible for applications like Kodi. Archive.org is amazing, but as a resource it's hard to use because it's not (as far as I'm aware) plugged in to something like TMDB to make it easier for the user to reduce their signal-to-noise ratio.
Thanks for your time and efforts, have a great day.