Yeah they had processor cards for Apple II's
en.wikipedia.org
Short answer no.
Why Apple doesn't want you to expand and prolong the use of your computer, they want to sell you more gear.
Just look at the lineup. No user replaceable stuff. Not even external GPU's.
The next version of the MacPro will be telling to see if they bless this system with expansion, but if they do you might as well give them your first born to them for the privilege, because it will be ridiculously expensive.
Also Emulation can take place of needing to run stuff.