I'd say yes and no.
Yes: There is always a chance that Apple announces a new iMac every month - just look at that MacBook Pros the past years, hardware updates almost came out of nowhere - without any schedule.
No: To me personally software support is bigger than the latest and greatest hardware - for the things you wrote any Mac will be great to use. And if you ordered your iMac right now, you can be sure to get all the latest software and OS version for the next couple of years without being left behind. There is more than enough power for every day use. If you were an professional creator there would be the need update almost every year. I still use a MacBook Pro from 2011 - back then I ordered it with the biggest i7 processor. About a year ago I upgraded the hardware with an 250GB SSD Samsung hard drive, maxed out the RAM to 8GB and put in a new battery. I'm stuck with High Sierra and as long as I get security patches I don't see any point to upgrade my MacBook Pro. Boot time now is 11 seconds, I'm still able to edit films and music in a acceptable time. Surfing the web, editing photos, syncing my iPhone and using E-mail still feels blazing fast. So you shouldn't worry too much - your new iMac will run way faster than my 8 year old MacBook. Apple Machines are great in longterm and as I wrote the chances a new version comes out is almost monthly.