why would anyone think that Microchip/Avr is any different or has any advantages compared to any other MCU manufacturer such as STM in terms of long term variability?
I agree. I don't know which one will be around longer. I assume they will all change. Today's STM32 will be tomorrow's Z80. Today's modern PIC will be the same.
In many cases, the only reason to not use the latest and greatest - when it actually can do the job at least as well if not better, and it actually is cheaper - is because of the learning curve. To a hobbyist, I suppose that just means more fun.
"Today's STM32 will be tomorrow's Z80" ... That's a epic quote because the Z80 slammed into industry's R&D departments like Orman's cannon slammed into the walls of Constantinople in 1453.
The Z80 reps dropped off beautifully written, free databooks and brochures and suddenly the Z80 was everywhere with STATIC registers that allowed the CLOCK to be slowed down and even stopped without data loss !
It was "Shock and Awe" and I was dazed and amazed. I later designed and made thousands of a small Z80 powered device that was coded with assembly on a TRS-80.
While nothing will replace the smooth as silk, orthogonal ISA of the 6800 for me, the legendary status of the Z80 is written in history, well at least my history.
I remember reading the Z80 databook in 1977 and thinking 'how can I possibly understand and use all these registers properly ?' and while the STM32F had a similar effect on me in 2014, good data books, ready product availability, constant coding and projects always reduce the new and unknown to the hundrum, at least for me.
I'm not afraid of the STM32 becoming unavailable, I'm afraid of becoming BORED with it
Finally, I'm not a hobbyist, I've worked as a electronics technician all my life, mostly in R&D assisting engineers and I've loved every single day. I've worked for engineers with zest, passion and foresight who loved what they did and inspired me. We all showed up at work at 7am and left at 10pm every day because the projects were our lives, nothing else mattered.
Some people work to live, I've always lived to work (in electronics).
And finally, to anyone reading this far. If electronics seems like work to you, and you hate the journey looking only to the destination every day .....
---------------------- YOU'RE IN THE WRONG PROFESSION, DO SOMETHING ELSE THAT EXCITES AND AMAZES YOU ! ----------------------