Not buying that, C64 had like 5-10 pcb revisions so spinning another one wouldnt be extraordinary, and in the mean time they could put bodges on old stock pcbs or you know, supply USERPORT cable as thats where 6526 is wired to. Original Kernal has no traces commodore ever tried to use hardware shift register, they simply left VIC20 bodge and didnt even try accommodating fixed 6526.