For small routers and networks, having MP/DC (dual-core) support as well as memory allocation control support isn't necessary, but think of the following in largers networks and routers:
1) Assign most functions to proc/core 1 and allow up to 256MB
2) Assign BGP and the associated WAN ports with 1GB RAM to proc/core 2
3) Assign (pick one or more) DNS/www/DHCP caching and xMB RAM to core 3
4) How about 1 core running the system and one running a large hotspot and NAT?
5) Assume that current model DS3 and OC-x cards get drivers, then those could actually have the power and memory to run. I say this as it seems that most of the "supported" devices are no longer in production.
Or, how about being able to just have a dual core system and divide the system RAM in half and then run as a live backup. This would allow one side to be upgraded and reboot keeping the other one live. Protection for a dead fan?
LOTS of options and capabilities. Being able to fully control the system would be most helpful.
Hope this helps to expand the horizons.
One reason MT gave for not making a list of running process available is that there are lots of features which share a single processes which would also make splitting them up between cores a difficult at least (Threads really shouldn't be migrated between cores and the schedular usually tries its hardest to make sure this doesn't happen for speed reasons).
Linux has a pretty good schedular (Better than Windows and arguably BSD as well as at least as good as Solaris) and good support for SMP (depending on the kernel version MT are using and how modified it is but both 2.4 and 2.6 have good SMP and scheduling) so there is no reason not to support it in some form.
The 1GB RAM limit really starts to hurt in dual-core/dual CPU systems where the RAM gets split between the CPUs. Linux has very good HIGHMEM support so there is no reason that >4GB can't be supported let alone >1GB. The 1GB mark has to be an artifically imposed limit and while there may have been a reason for it in the past it is hard to see why it remains.
Another pain of the 1GB max limit in a SMP box is say you are using 2xOpterons and you give each one 512MB RAM to max out RouterOS. If you want to have that dual channel you need to find some 256MB sticks which are becoming rarer, particulrarly decent server grade stuff. You are also leaving a huge number of slots unoccupied which is just a waste.
As for splitting a system for redundancy I don't know of any x86 CPUs that are able to run in AMP (Asymmetrical-Multi-Processing - It is mostly specialist industrial and automotive CPUs that are). The only way I can think of to do this is virtulisation (i.e. Xen - which I would actually like to see for reasons I outlined in another thread)