Amiga OS 3.9 supports many of the things you mentioned, others are best prvided for by 3rd party Amiga developers. It is not to good to have to much bloat in the OS.
3D acceleration= You need a PCI adaptor for Amiga to take advantage of this but just use Warp3D. Some people use a CubervisionPPC but this gfx card is not as fast as some of the latest supported via the Mediator PCI adaptor. Amiga has had 3D acc. since the release of CybervisionPPC back in 1998.
multiprocessing= My Phase 5 card runs an 060 & PPC at the same time. Sure I don't have two or three PPCs running but Amiga owners would only need this if they are doing complex 3d rendering. If that is something you have to do then a 64 processor or 128 processor Sun Box with Lightwave 7 is your best bet. Or the fasstest machine you can afford running Lightwave 7. The Amiga OS is a realtime OS and does not need lots of CPU's for general computer stuff. My A4000T switches between apps much faster than my 1.2Ghz AMD Windows XP crate. True I only have one CPU but it is going 1200 Mhz! My Amiga is only going 50Mhz with the 060 unless I run a PPC app or MorphOS.
virtual memory= Aminet has free solutions for this and the Amiga has had VM apps for sale for years. Even ImageFX has built in support for it. The question is why would anyone want VM built into the OS? A Harddisk is way to slow to be used as RAM, VM has been slowing Windows down for years. Memory is dirt cheap so who cares about this?
PC compatiblity= Commodore had hardware solutions for 286 & 386 (the bridgeboard) but Amiga owners did not care. The Amiga was one of the first computers that had emulators. The A1000 had a software XT emulator and AMAX was avail early in the Amiga's life (Let you emulate a Mac). They have been many others over the years like the Golden Gate 486 from Germany etc. MorphOS even has a port of Bochs
so we have been doing emulation for years, sure the PC is doing it now as well but the idea came from Amiga.
scanners/cameras= German apps like ScanQuix have great scanner support. ImageFX supports SCSI scanners and their are several apps the support diugital cameras, sure its not in the OS but it is avail from Aminet and 3rd party developers. That is one of the cool things about the Amiga, the great 3rd party developers and Aminet. Here are a few examples.
Again I don't want this in the OS, it is better as an add-on solution for those that need it. An OS needs to be fast, lean and mean.
Weird joysticks= Well Amiga has had it 's share of weird joysticks over the years we just did not need drivers for them. The Gravis Mousestick was a good example. Hell I even have an adaptor that lets me use Playstation joysticks (PSX Port).
You can use almost any PC joystick you want on the Amiga if you have the adaptor, several different ones are sold. Wireless keyboards and other devices like wheel mice can be used as well.
memory protection= This would be a nice add on for the Amiga OS, Aminet has a few but I have not tried them. MorphOS already supports this.
better-than-stereo sound= Add a soundcard like you have to on the PC, Amiga stock sound is a hell of alot better than PC speaker. The Amiga has had some cool sound cards over the years like Studio16, Flyer, etc. REPULSE seems to be the soundcard Amiga owners are buying today.
Or if you have PCI in your Amiga just go to CompUSA and buy whatever high-end Soundblaster card you want.
playing music CD's= Amiga OS 35 & 3.9 include this but Amiga has been doing it for years. Look at the 1990 CDTV, one of the koolest CD Players you will ever see. Even a PS2 does not have an interface as nice as the one Jim Sachs made on CDTV & CD32.
tape backup= I was doing tape backup in 1991 via a 250MB SCSI tape drive, work fine for me but tapes are slow. Most people don't use them today. CD-R/CD-RW DVD-RAM/DVD-R/DVD/RW has taken over. The Amiga does not support DVD-R/RW yet, you should have brought that up.
zip drives= been there done that long ago, support is also built into Amiga OS 3.9
music generation= The Amiga was the gifted with the tracker and mods long ago. Soundtracker, Octmed etc. We also had the very cool Bars & Pipes Pro and SoundJam. B&P was so cool M$ snapped up that company but the code lives on as open-source on the Amiga. Mods were the MP3 of their day.
Windows XP= Includes stuff Workbench 1.0 had! The Say command and male/female voice based on what you type. It is better than what we had in 1985 but not by much.
AREXX= Windows is a ocean of everyone reinventing over and over.
I don't find that Windows apps have anything like AREXX, so much weird stuff is supported based on what company made it that developers don't know what to code to as far as scripting goes.
Newtek got it right on the PC with George in Aura and LWScript in Lightwave 7. But these are just types of AREXX.
In Amiga OS 3.9 even Workbench does AREXX.
pre-yesterdecade's hardware= My Amiga has the latest PCI cards that I picked up at CompUSA. Amithlon owners are running on the latest hardware as well although I still like real Amiga hardware with PCI added, so stuff like the Video Toaster Flyer, Phonepak & Studio 16 still work.
Printing= Something you left out, the Amiga OS does not support newer printers.
Thats why you need the ever cool Turbo Print!