Historically, subsystems (drivers, etc.) were supposed to deliver on both SPARC and x86 platforms (and now amd64 as well) unless a really good argument was supplied. While I've long been a supporter of this philosophy, I think a time is coming to consider making a specific policy exception.
The problem I'm running into is with legacy PCI devices. Some of these legacy PCI devices can work SPARC. But devices that don't support 66 MHz frequently (but not always) have problems on SPARC workstations. The biggest problem is that many SPARC workstations have 32-bit 33 MHz slots that don't supply 3.3V. This affects quite a number of cards that require 3.3V power to operate. Some devices will operate with only 5V, but only marginally. I've seen a number of failures that I think can be traced to this problem, and now I don't recommend using PCI devices not specifically qualified for these platforms with SPARC systems. (Sun makes that same recommendation, btw.)
Furthermore, identifying suitable SPARC hardware can be a challenge. SPARC systems these days are slower than their x86 counterparts, yet for the most part remain more expensive, and there are few inexpensive options available for open source developers. And, SPARC desktop systems are effectively off the market -- Sun doesn't have any current SPARC desktop models for sale, and that's not likely to change anytime soon.
So what I'd like to propose is a policy change that recommends authors working on drivers for legacy PCI cards be given a blanket waiver for SPARC delivery. (Examples are recent NIC drivers such as "vr", "sfe", and "bfe", and audio hardware such as "audiopci", "audiocmi", and perhaps in the future drivers for Creative Audigy cards.)
I still believe that developers working with modern PCIe devices should deliver both SPARC and x86 binaries though. PCIe is available on last generation SPARC desktop (Ultra 25/45) hardware as well as current generation server products.