do they seem unfeasible?
Short answer: yes.
1. better CPP
I make well over 50% of what the customer pays for most of my papers. The rest goes to operating costs and the owners' profits. Yes, the site owner probably make more each year than I do, but that's what ownership is all about. I plan on being an owner of some sort someday, and am not a Marxist.
2. bonus system for repeat customers
The bonus comes in the form of guaranteed work that other writers aren't able to take. If that doesn't exist for you, the companies you work for suck.
3. royalties system
This would imply that writers still retain ownership of their written materials, which is counter to standard freelance work-for-hire contracts in all industries.
4. paid sick days, from a formula based on the writer's average output
A. I can work when I'm sick. B. I make enough on the days I choose to work that I an take many more days a year off than I need to for illness. C. Paid sick days would necessitate lower wages on days that I do work, basically giving me the same level of pay but less control over how/when it was earned (I'll dismantle your finding suggestions next).
1. take less % of the cut
Well, duh. But why should any successful business owner not reap the profits of the business they created and continue to maintain as long as they are treating their employees fairly? This has been the crux of your disagreement with other writers--you take it for granted that writers are being treated unfairly, but at decent companies you can earn A LOT of money doing relatively easy work whenever you feel like doing it. This seems like a fair shake to me.
Tackling the problem form a different direction, most successful restaurant owners (including hugely profitable chains like McDonald's) could afford to cut into their profits to pay their employees more. They don't. because their employes are content with the wages they earn, or the move on. This is the way markets work.
2. pay repeat customer bonuses from the advertising budget (customer loyalty is the goal of advertising, anyway)
Advertising "budgets" for these companies are very small--it doesn't take a lot of money to market these sites, it takes a lot of time. The same admin that deal with marketing (i.e. SEO) also deal with customer service, usually, and the "budget" is relatively non-existent. This would also mean less money spent attracting new customers, which form by far the largest demographic of customers each year.
3. put aside a fund for writers from pre-written paper income
Again, this isn't increasing pay at all, its just redistributing it. Why would I want the company to keep part of my money now so they could pay it to me later? I'm good at saving and investing; I like my money to be paid at the time that I've earned it.