Cue the should I buy or wait comments in 3.. 2.. 1..
These "should I buy or wait" comments for the 2017 iMac have been around since at least the end of last winter. Some people were suspecting a 2018 iMac as early as spring time.
I posted back then that my thoughts were that Apple probably wouldn't have a 2018 iMac until really late, or maybe not until 2019. Anyone that is still waiting might still have a long wait ahead of them.