Charge more for LTS support. That’ll chase people onto your new systems.

I’ve seen this play out badly before. It costs real money to keep engineers knowledgeable of what should rightfully be EOL systems. If you can make your laggard customers pay extra for that service, you can take care of those engineers.

The reward for refactoring shitty code is supposed to be not having to deal with it anymore. If you have to continue dealing with it anyway, then you pay for every mistake for years even if you catch it early. You start shutting down the will for continuous improvement. The tech debt starts to accumulate because it can never be cleared, and trying to use makes maintenance five times more confusing. People start wanting more Waterfall design to try to keep errors from ever being released in the first place. It’s a mess.

Make them pay for the privilege/hassle.

Models aren't code though. I'm sure there's code around it but for the most part models aren't maintained, they're just replaced. And a system that was state of the art literally yesterday is really hard to characterize as "rightfully EOL".

Two diffetent models can not be direct replacements of eachother. It's like two different novels.