Moore's Law and the limited demands most users have on their systems will mean an iPad-sized device will have the power to run 98% of today's workloads. Even today the iPad's limitations are mostly software, not hardware.
Docking station deluxe
Apple is already shipping the how: the 27" Thunderbolt Display. With a single cable to the display users get a gorgeous higher-than-HD 2560x1440 display, Gigabit Ethernet, FireWire and USB ports, and a 40Gb/sec Thunderbolt port. Roll into work, plug in power and Thunderbolt cables and a Thunderbolt array and you've got more computing firepower than most workstations did 5 years ago.
Put a Thunderbolt port on a future Even Newer iPad and you're good to go. That's the easy part.
Most skeptics call out applications such as video editing - rendering, actually - music production and tech apps such as computational fluid dynamics as reasons that masses will never replace desktops and notebooks with tablets. But the masses don't use those apps today and they aren't about to start.
The most common corporate apps - Microsoft Office, email, browsers and project management - can be handled by any 1 GHz x86 or ARM processor. That's why notebooks are taking an ever larger piece of the market: even with slower processors, disks and smaller displays, they can do the jobs that most people need done.
Moore's Law is still doubling transistors every couple of years, and innovations like 3D chips are aiding performance. At that rate the current A5x dual-core processor in the New iPad will be a quad-core and twice as fast in 5 years.
NAND flash is also getting cheaper. So a 2017 iPad could have 256GB of flash storage - way more than what most people use - and 4GB of RAM for the same price as today's New iPad.
I experimented with using an iPad to replace my notebook. It didn't work for me - but not because the hardware was too slow. A multi-tasking OS is required to flip from writing to research to mail to Skype to photo editing in a timely fashion.
True, transcoding and rendering video is slower than I'd like even on today's MacBook Air. But the rest of what I do is just as snappy as it is on my quad-core I7 iMac - or snappier - thanks to the MacBook Air's SSD.
Where the MacBook Air is today, the iPad will be tomorrow.
The Storage Bits take
Desktops and notebooks aren't going away. But for the mass of consumers and corporate workers a dockable iPad with a multi-tasking OS and a larger external display will be all they need in 5 years.
If Apple can retain its current tablet market share - as they did with music players - they will own the PC market in 5 years. Soon Wintel's reign as kings of PCs will seem as quaint as IBM's '70s-era domination of the computer industry.
Comments welcome, of course. For heads-down computer workers - like me and, I suspect, many ZDNet readers, a stable and powerful workstation will always be preferred. But we're a tiny minority of computer users.