Why not just add a section for "machines designed for AmigaOS 4"? It won't take away anything from the rest of the site; if you don't want to see machines like Sams and X1000s just don't go into the new area.
It's not like there's anything sacred about 68k Amigas, they're all just machines designed to run AmigaOS on, or machines that were chosen to run AmigaOS on in the case of the A1XE: that includes 68k and PowerPC.
I would also include machines like the Peg 1 and 2 and Efika for MorphOS and the AROS machines like the iMica, but I would stop short of including generic PCs and Macs because they're covered by other websites; you have to draw the line somewhere, after all.