I certainly can't think ahead 20 years but I think it's safe to say that the next 5 (at least doing HPC and large-scale web type stuff) will increasingly look like this: http://www.technologyreview.com/computing/22504/?a=f, which talks about building a cluster from AMD Geode (!) nodes w/ compact flash storage. Sure it's not super-fast, but it's very efficient per watt. If you had more cash you might substitute HE Opterons and SSD's but the principle is the same.
The general trend is that capital expenditures for computing are going down but operating expenditures are going up. Indeed if you sign up for something like Amazon's EC2 service, your initial capital outlay is exactly $0. (I vividly recall paying over $3000 for a low-end server and $300/month in colo fees back in early 2003 when I had a hosting business.) Apparently they use the above cluster to implement some type of distributed memcached style cache. Here is the page listing the many clients for memcached: http://code.google.com/p/memcached/wiki/Clients. However, if w/ Plan 9 you implement the interface to the cache as a 9p service, it is automatically available to any language that can do file I/O (heck, even Haskell, if you can slog through the advanced type theory). So your software development costs go down. Another change that levels the playing field in Plan 9's favor is the clock-speed wall and the move to multi-core chips. Soon everyone is going to have to re-write their software to make it concurrent if they want to make it run faster. And concurrency is hard, especially when the predominant model is preemptive threads. Here again Plan 9's technical advantages of its lightweight kernel and CSP threading model confers an economic advantage. I think the key to successfully being able to use Plan 9 commercially is to use its unique technical advantages to exploit disruptive economic changes. Economics beats technology every time (e.g., x86/amd64 vs. MIPS/Itanium, Ethernet vs. Infiniband, SATA vs. SCSI) so don't try to fight it. John
