It hasn't declined any more than pepsi and coca cola have declined, and there's no reason to believe it ever will. MIPS is gone. Power architecture being open sourced likely means IBM no longer has a business interest in it. This is what business folks call shakeout. It's what intellectuals would call the "end of history" for the microprocessor, similar to the fall the USSR. Big money research has moved on to quantum processors.
Speaking as someone who's an avid reader of open source codebases, I kind of wish more of my colleagues would accept this, because it really stymies progress in open source that folks continue supporting huge amounts of code that today are mostly only used by folks doing things like emulating Sega Saturn on an FPGA for fun.
Speaking as someone who's an avid reader of open source codebases, I kind of wish more of my colleagues would accept this, because it really stymies progress in open source that folks continue supporting huge amounts of code that today are mostly only used by folks doing things like emulating Sega Saturn on an FPGA for fun.