For creators, some sort of unified treaty about copyright reversion. This would probably go over good in Berne convention aligned countries because follows moral rights philosophy.
One of the main problems with copyright is actually the DMCA, so fix the DMCA to not make it so easy for people to squash things.
finally people have a problem with the term limits of copyright. This is a hard thing to fix, basically I would think the copyright of works is a little bit of too long now - I would say 60 years or the life of the creator whichever is longer. For companies obviously has to be 60 years then. So someone writes a book at 20 and lives to be 85 they have 65 years, someone writes a book at 65 and dies at 67, the book remains in copyright 58 more years after death and their kids get taken care of if that book happens to be the best selling children's book of all time or something like that.
Characters created in one work etc. are copyrighted from the time of their first creation.
for creators as well, lighten or get rid of registration requirement in the U.S (which is required in order to sue for infringement and needs to be timely in order to get statutory damages) or course no European court has this, because Berne convention, so I think it would be nice to align things.
Why your plan to fix copyright won't work:
1. It does not take into account the different understandings of the purpose of copyright in other countries than the U.S.
2. It makes things more difficult for the creators of copyrightable works, and makes it easier for unscrupulous individuals to take advantage of creators of copyrightable works.
3. It makes things more difficult for small companies, meaning that bigger companies will be able to take advantage and increase their power.
On the first point, the understanding of the purpose of copyright in the U.S is that it is promote the common good, in the EU the understanding is that it is to protect the rights of people who have created something and have a moral right to ownership of the thing they have created - based on the Berne convention https://www.wipo.int/treaties/en/ip/berne/summary_berne.html of which by the way the U.S is a signatory.
At any rate your fee setting and registration rules perfectly aligns with the purpose of increasing the common good, but does not align very well with the moral right to ownership of ones work. Now before when the U.S increased the copyright term limits obviously countries that believed in the Berne convention were willing to sign on to that because increasing the term limits can theoretically be helping the creator of a work (although in practice probably not) but all this other stuff not helping will mean if your rules were enacted in the U.S the international structure of copyright would have to fall apart.
On the second point, why is it difficult for creators of copyrightable works? Well, unfortunately not everyone is good at everything and it has been noted in the past that many artists, musicians, writers are not especially good at organizational skills and as such are often liable to get taken advantage of by unscrupulous people who are good at these things. Do I have to provide links to examples of this happening, or to the assertion that people in the creative professions are often lacking on the organizational front or can this be taken as a given? As such putting another thing they have to manage and they will have to keep managing for as long as they want to derive any profit from their labor on their plate is going to increase the chance of their being taken advantage of. Someone will now undoubtedly say but they will just hire someone to do it for them, which will be forestalled hereby by noting you have to be doing relatively well from your labor to afford to hire people to take care of these kinds of things for you (and this of course will keep some people from doing well enough to hire the persons needed to help them), and even if you are you can get ripped off by the people who are supposed to be helping you organize things.
On the third point, smaller companies will have trouble doing this has already been handled in the comments.
> If you have multiple works in one product (think Marvel movies) then all revenue goes to the oldest work (that way you can't avoid the fee by putting new and old characters together).
so a work is no longer a book or a movie, but a character?