Wow, lots of questions. Here's my take.
We agree that tape is a pain for the SMB. Few people need to archive at that price!
A ReadyNAS can replicate offsite to another ReadyNAS, which is a great solution for synchronizong a single copy of your data. As we build more business models we are looking at offering replication with a secure component so you don't need a VPN to move the data safely. In addition, we may look at optional offsite archive services in the cloud, so you can pick what you want to keep, let the ReadyNAS dump it to a datacenter at night and pay by the GB. No more tape, native recovery formats and multiple layers that can be implemented on one single platform.
Restores to non-identical boxes is the holy grail and I think it is here today for a VAR that can learn VMware, Citrix XenServer or Microsoft Hyper-V. Storing your desktops and servers as virtual machines on a ReadyNAS means instantly starting up a new client including OS, settings and apps. Our iSCSI beta release went up on the forums today and if you have a Pro you should try this out. BTW, this is where data deduplication technologies really prove their value and earn their prices!
RAID 6 is far more cost effective than RAID 5+1, and I'm sure that will become the SMB standard as drives get larger. See the thread around here on disk drive capacity and rebuild times.
As far as interfaces, the fast one are expensive. I can think of Infiniband (no way), SAS (still too expensive) and eSATA. eSATA is gaining traction but nothing is as universal as TCP/IP for getting offsite, so I think your choice is to look at investing in the WAN or in local capacity. A second ReadyNAS as a target may be more cost effective than upgrading your WAN gear. Some VARs are considering services that move data from small ReadyNAS in the field to a larger centralized model for a montly fee for their customers. Smart networks will use multiple NICs on their switches to segment traffic and that's an important feature for a business-class storage system (and switch, for that matter).
I get my energy from the sun at home, but I still hate wasteful devices. Power supply choices are purely cost-driven for us but the RAIDiator feature that schedules my system power on/off cut my home ReadyNAS consumption in half and probably doubled the lifespan. That's good ROI for anyone!
Hope this helps, and feel free to disagree,