It seems to me that a business should step into the desire of countries for proof of onward travel. There are many times an onward ticket is not sensible. The countries are worried about people staying and/or become drains on the economy it isn't that they care about having a piece of paper saying you have a ticket out. A business could step in to aid travelers and vouch for people's financial well-being. A long time ago I believe American Express offices were actually used a great deal by travelers. It could start with companies like American Express.
They could provide a financial guarantee. Countries mostly would be thrilled to encourage visitors who are "wealthy" (globally wealthy people may well not think they are wealthy). Credit card companies could make it a feature of gold cards for example...
Digital nomads and location-independent workers often travel one country at a time, without onward travel confirmed. When I was I didn't know how long I would want to stay or where I would go next. The way things normally work, they are much looser with passports from rich countries, and since I have one, I didn't have problems. But as rules get more demanding it could become more annoying and it already is if you have a passport that isn't desired.
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