Every architecture is good for different things. ARM beats MIPS for doing math but MIPS beats ARM for networking. When you want VPN and configuration complexity PPC beats the lot but x86 is still the fastest in all catogaries. Bit count dont really matter though except for high bit count encryption if there are no accelerators. You will see the broadcom ARM A9 beating 32 bit MIPS routers but in truth if you were to pit them together with the same clocks and the same cores you will find that the MIPS 24K is faster than ARM per clock in networking.
MIPS has it's strengths - but these days, with the consumer grade SoC's, the chipset vendors are looking at getting more chips from a wafer, and the older MIPS blocks didn't scale down to smaller geometry nodes - so as vendors did their die shrinks, the Cortex-A9 (or their own inhouse ARMv7 cores like Armada/Krait) made a lot of sense...
Going upmarket, MIPS still has a very strong presence in the SME space - Cavium is a great example here...
PPC - Two main vendors out there - AMCC and Freescale - AMCC seems to be more focused on legacy support for embedded designs that other PowerPC vendors have walked away from (and doing good business there) and then with Freescale - their PPC QoIRQ chipset tend to be focused on specific verticals - and they're pretty spendy compared to what is found with MIPS/ARM - but I agree, PowerPC, while not having huge success in certain market segments, are very powerful solutions
X86 - AMD/Intel pretty much - would be nice to see one of them jump into the Consumer AP/Router space, but their attention is really focused on other segments - Bobcat/Jaguar/Puma (AMD) and Silvermont/Airmont (Intel), we see them in NAS and Mediaplayers - and AMD's success with XBone/PS4 is well known - The Dual/Quad Intel Silvermont (Airmont) SoC's - in the SNB space, they're typically in NAS boxes and STB's, along with AMD's G-Series (Puma cores with a lightweight GPU).
The big challenge with the Intel/AMD small cores is pricing - typically the SoC's run between 75 to 105 USD, which is plainly too expensive for a consumer grade Router/AP - compared to Cortex-A9 (and MIPS) solutions in the sub-$20 range...
Intel does have one X86 core (other than Quarks, and nobody should go there for a router/AP) that is sub-20 bucks - and that is the Z-series Z-3735G, a table chip, which loses PCIe, SATA, USB3 and enables only a single memory controller - not suitable for a Router/AP - however they work great as STB processors in the mini-PC realm (they boot Linux/Android/Win8, 10 in 32bit mode) and run great multi-media apps (KODI, Plex, etc) and do it well... note that Intel is discounting that chip signficiantly compared to other Quad Silvermonts (to the order of about $60 a chip) as they're all pretty close die size wise..
I would really like to see Intel jump into this space, but since they're already pulling shedloads of money from the market segments they're in, it's their call perhaps... but if they put their mind to it, it would be a compelling solution.
Going into 32/64 bit - mixed bag, but generally 64-bit in ARM/X86 do offer advantages over their 32-bit ancestors - better/newer instruction pipelines, more registers, better capabilities at memory management and manipulation...
I do think, that sometime in 2016, we'll likely see a Router/AP System on Chip that is 64-bit - and most like ARMv8 based - could be QC/Atheros, or Broadcom perhaps, and don't rule out Marvell..