No kidding a Surface Studio-like iMac will jack up the price.I had mine for 6 years (started with the 2011 27" iMac). Worked great, and finally just wanted something better. So long as specs isn't an issue, you should be able to hang on to it for 6-7 years at least.
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An imac with such a feature is going to jack up the price significantly, and be such a niche product category that it will likely not sell enough quantities to justify the R&D.
If it's art you want, you can consider the 12.9" iPad Pro. Even the guy from Penny Arcade is using it for his work.