To be fair, it's not like this isn't standard industry practice. Airframe evolve and change, with incremental changes typically only affecting limited areas of impact.

OTOH seeking a non aerodynamic solution to a significant stability degrading airframe modification was IMHO a bridge too far. If the pitch stability (not the pitch feel) problems couldn't be dealt with aerodymancally without busting type certification, than perhaps the whole concept was just too much of a stretch for the venerable old 737.

It surprises me, though, that this couldn't have been engineered out with enhancements to the horizontal stabilizer, such as tip fences or a span increase to offset the lift from the engine nacelles.

If it could have, but software was cheaper, then that's even a darker indictment of Boeing's engineering incompetence.

Re-engineering the rudder may also have helped avoiding employing pitch control (with it's inherent delay and hard to undo actions). But that would have made it obvious that this is a different plane...

If you make the plane wider you run into issues finding room for it at the gates.

The FAA needs to grow a pair and declare this type certification and all other certifications older than ~30 years EOLed. That doesn't mean you can't continue operating those planes, it just means you can't retrofit some changes onto a deeply legacy model and still call it the same type.

I think its not about retrofitting and more about retrofitting (engines in this case) in the wrong place.

Say what now? It sounds like you want the FAA to revoke the A320 type certificate?

Yes. The A320neo should be the last new design allowed under the same certification. They'll be forced to re-certify whatever they do next anyway, so they won't have to try to shoehorn things into the older design like Boeing did with the 737.

But Airbus shoehorned the same thing - a CFM LEAP - into an older design, just like Boeing did.

It's not the case that they won't have to try, they already did it years ago.