I earn little enough without paying any more costs. So no to both. I think there would also be questions of copyright as many agencies require the submitter to own the copyright and I'm not giving that away. I would also want some pretty strong assurances about my control over my images and the trustworthiness of any such organisation.

No, and absolutely no.

No one will ever care more about my clips than myself, and let's be honest here, someone working as a clip tagger will not be the most "talented" person in the world.

Furthermore, they will not know where, when, how, why the clip was filmed without that information having to be provided by the creator anyway.

No, and I don't pay another agency to do my key wording.  All processing and preparation is done by me, so it costs only my time.  Using your model (or ideas, I lose even more with an already anorexic microstock biz.  I don't think you'd ever find enough people to successfully run a business outlined in your post. Any fee, no matter how small, is too much.

Would you consider acceptable for an agency to sell your stock content on all major platforms given that you only need to provide the content (no need for metadata, keywords and other details to be filled)? Or instead you would prefer to pay for tagging service and upload by yourself? In the first option, you will pay a small fee per sale.

Look at BlackBox for videos. They have a ton of people picking them up for doing about what you suggest.

One change though.  They negotiated a higher payout with the agencies because of their huge volume.  After only 3 months in business, they already have almost 100,000 video clips on Shutterstock, and BB says that the other agencies have higher number yet, with SS being one of the lowest.

BB charges 15% of the received royalty.  However, their payout is sufficiently larger than most humans could obtain, that the amount you receive from a BB sale is actually larger than a direct sale to the same agency.

Now... if you could arrange that (a higher payout than I get by going direct) AND you could address all the major agencies (first and second tier), then I might actually consider your service.

Otherwise, no.  It just isn't all that hard submitting photos to the agencies myself to give a part of it up to someone else.  (Videos are much harder to upload, partly because of file size and partly because keywords, titles, etc are not part of the video format, so must be copy/pasted for each clip for each agency)

Would you consider acceptable for an agency to sell your stock content on all major platforms given that you only need to provide the content (no need for metadata, keywords and other details to be filled)? Or instead you would prefer to pay for tagging service and upload by yourself? In the first option, you will pay a small fee per sale.

No. Commissions are so low already, and the % agencies are taking is sky-high.

Plus, as tedious as keywording can be, I want to keyword my own images.

Would you consider acceptable for an agency to sell your stock content on all major platforms given that you only need to provide the content (no need for metadata, keywords and other details to be filled)?

this is called production agency: f-stop, imageSource, cultura creative, etc