Install Windows 10 Creators Update on iMac11,2 without first installing Windows 8
There's a difference between the Microsoft &amp; Apple definitions of "support". 

If Apple says it's unsupported that means there are no Windows 10 drivers for your hardware.

Whether that is a minor inconvenience or a catastrophic fail you'd have to try it to see.

The difference in definition isn't only an Apple/MS distinction... MS allowed people on regular Windows PCs to update to WIn10 even though Intel themselves weren't making drivers available for their hardware.
At least Apple are telling you up front you will have no proper hardware support.