For making Windows 98 usable on much newer hardware than it was ever designed for, here's the major drivers that are still missing:
- A proper fix for the "Crazy Mouse" bug when using legacy USB mouse support on certain BIOSes. This seems to be caused by vmouse.vxd or msmouse.vxd losing framing when reading from the emulated PS/2 IO port, and can be worked around by using a Windows 3.1 16-bit mouse driver though this still causes other issues like mousewheel and mouse in DOS not to work.
- Support for newer wireless network adapters supporting WPA2. SDZ recently backported a NDIS network driver for Intel gigabit controllers from ReactOS so maybe this is a place to look.
- Better 3d graphics support then is available through VESA and SoftGPU. There are a couple of ways to approach this and JHRobotics seems to be working on one part already by creating a library to allow Mesa to use multiple CPU cores for rendering. It might also be possible to backport a legacy version of Mesa's OpenGL driversto be able to GPU accelerate the rendering on much nerwer hardware though this would be a massive amount of work.
- ACPI power management support on newer machines. This would be very complicated, and there is probably no way to support the IOAPIC or Message Signaled Interrupts because of how the system architecture is.