Looks like IBM and Apple have tried the 64-bit thing as far back as 1991 [pdf]. Wonder if OS 9- ever looked at being 64-bit native?

Here's a quote:
Contrary to some reports, the 970 isn’t the first 64-bit Power- PC. In fact, a 64-bit PowerPC was planned from the start, when IBM,Motorola, and Apple began creating the PowerPC architecture at the Somerset design center in Austin in the early 1990s (MPR 7/24/91, “Apple/IBM Deal Catapults RS/6000 to Prominence”). At that time, the PowerPC alliance promised to deliver three 32-bit processors—the 601, 603, and 604—and one 64-bit implementation, the 620. All four chips eventually reached the market, but only the 32-bit processors succeeded. The ill-fated 620 first appeared on the PowerPC roadmap in 1991 and was first described at Microprocessor Forum in 1994 (see MPR 10/24/94-02, “620 Fills Out PowerPC Product Line”), but it didn’t ship until 1998. By then, it had grown so complex it was uneconomical. At 250mm2, it was Motorola’s largest slab of silicon. The 620 never made it into a Mac and soon vanished.