Why bother with wifi? The Shinkansen are so fucking fast, you'll almost be at your destination by the time you've unpacked the laptop, found the right power adapter, plugged in your mouse, got past the captive portal, etc, etc.
The Japanese offering has always beaten ours. With or without wi-fi. Their trains are fast, comfortable, punctual, clean, have civil staff, etc, etc. I'd choose a Shunkansen over Scotrail every time.