SCOM 2007 R2 Scalability

SCOM 2007 R2 Scalability - SCOM 2007 R2's scalability is clearly exceeds that of its predecessor but exactly how big can it scale? Due to limitations of the RMS, specifically the instance space....the maximum number of agents (servers & devices) is 10,000 per management group. With the recent release of cross-platform extensions and desktop support it seems that large enterprises who wish to deploy to serves, networking devices and desktops are limited to 10,000 per management group and would be forced to a multi-management group scenario. The purpose of this discussion is to see what kind of strategies you may suggest to expand beyond 10,000 objects while maintaining a fairly efficient user experience. Consider the following scenario for a retailer located in say North America:

High Level Design
-2200 Stores -  Approximately 249,800 Servers/Devices:
-109 devices per store: 
  *9 servers - (3 Win / 4 Linux / 2 ESX     servers)
  *70 PCs  (PoS on XP)
  *30 SNMP devices
Corporate Datacenter with 10,000 devices (8000 Windows, 1000 Linux and 1000 SNMP devices)

Design Considerations / Questions:
*What would you use to monitor the non-Microsoft servers and SNMP devices and why? (xplat, Quest, Jalasoft, other etc.)
*What is the delta in load on the RMS between 1 Windows 2003 server vs. 1 Cisco router?
*Can you design effectively with less than 25 MGs?
*How would you deliver a central data warehouse solution?
*Of the 154,000 PCs which are basically cash registers, what would you monitor? *The PoS solution does not have an In-Store Processor unfortunately?

Ultimately, the number 1 design goal is, assuming you can make it work, simplicity. We do not want to have to hire 100 additional support staff just to maintain SCOM. Go nuts, this is just a community brain storming session.