For now, but edge computing diminishes the role of the mainframe. This makes it easier to replace the mainframe. Eventually someone will do that.
Previous PCs came from chips and designs that were originally built to power terminals for mainframes like the Intel 4004/8008, the 6502, and the Z80. Today's handheld dumb terminals for mainframes are built with ARM64 chips that are approaching "desktop" performance levels just like those old dumb term chips started to approach useful performance levels before someone realized you didn't need the mainframe anymore.
... and so the wheel turns.
I think the biggest current barrier to de-cloudification of mobile devices is the heavily and cryptographically locked down OS. That's a software thing, not a hardware thing.