Just a quick question: when entering countries in Central America, did you guys need to show onward tickets? In theory, we all do (even if from EU, USA and the such), which is why, government owned airlines wouldn't sell me a one-way ticket. Once I get to Guatemala, I'll continue by land, which should be easy with no onward ticket. But how to get to Guatemala on a one-way from Europe or Cuba is a problem. Any ideas? Thank you!

Try a different airline. TACA folks are ticket whores. I'm from the US and in multiple trips over the decades....the second this year is coming up... I've never been asked for an onward ticket either by land or air.

You should not have any issues with Immigration, other than Panama, at the border they may require you to buy a $6 return bus ticket.
Overall, its the airlines enforcing these restrictions, and the countries immigration. You should be able to buy One way tickets to EU and or Cuba no problem. The ticket offices will know whats the deal is. There are flights to Havana from Mexico, Managua Nicaragua, San Jose Costa Rica and Panama City Panama.