I've heard there are a number of things, like the action economy, that can be easily adapted from PF2. But overall, I think how Everything has been feat-ized is a deterrent.

If you're interested in a "D20-Modern-For-5e", I recommend Amazing Adventures 5e. It's exactly what I want in a "modern" game, and fully compatible with 5e. Classes and such can be interchangeable. Pretty cool!