CodeIgniter 4 Important Features

I think it's a waste of time focusing in compatibility layers unless it's really easy to do.

Let's say I have 100 CI projects. Why do I need to migrate to CI4 all of them? Even if it's easy it will be one more source of trouble. From the old CI projects only a few will justify to migrate probably. And those are probably important projects that need to keep evolving.

Those who don't need to keep evolving will die sooner or later. If you are not developing it in a consistent way why worry about migrate it?

Basically this is my point of view. Some things don't need to evolve and others do. Whatever makes the evolution quicker and better it's very welcome. If compatibility layers and so on will turn CI4 better so be it, if they are only stalling and serving a very small minority of cases then just forget about it and let evolution take control