BS Node 2i: WiFi or Ethernet..?

It's about noise and the designer of any given streamer. It varies.   

Wired ethernet -and- wireless connections introduce noise.   

Look up Signal-to-Noise Ratio (SNR) and Wireless Signal Strength.

Also, ref: https://darko.audio/2018/08/ethernet-or-wifi-which-is-better-for-high-end-audio-streaming/

Ian Mark the Steve Hoffman piece you sent was from soeone who doesn’t know much about  compiter Audio and a dac like the quest will sound far better running usb Mr Hoffman used aes which will not sound as good for more modern dacs designed for high res where usb will sound better

I have. Easy to do.

I’ve used my Bluesound Node 2i with both wifi and connected via ethernet and I’m hard pressed to notice much of any difference in quality.

My internet setup is the last generation Netscape Orbi and I compared by running ethernet from one of the satellites vs connecting via wifi which can come from satellites or the router depending on network traffic

Also, I'll echo what was said above - the biggest upgrade to the Node 2i was the power cable; 
I found my favorites to be a $10 Hosa cable from Amazon US to the $240 Acoustic Revive Absolute Power from Amazon Japan. Ultimately, I preferred the Acoustic Revive but the Hosa is better than some much more expensive cables I tried.

Ethernet wired connection will ALWAYS be better. It will always provide a more reliable medium.

If wifi works perfectly, there will be no difference. However, since wifi is almost always prone to distance and/or interference and connectivity issues, it will always be inferior to ethernet wired connectivity.