It is an unfortunate reality, but our engineering resources are limited, and we have chosen to concentrate those resources on supporting the BeOS on Pentium-or-better processors. We have our hands full (and then some) just trying to support a broad range of modern systems.
The reality is that the number of 486-based systems is not growing (indeed, it is likely shrinking, as they are replaced by newer systems), while Pentium-or-better systems are selling like crazy.
You can buy a complete 200+ MHz Pentium II system today for well under $1,000, and even systems costing as little as $500 outperform 486 systems. Investing in better hardware will improve the performance of all your software, for all operating systems, not just the BeOS.