Any “value” competitor streamers vs Bluesound Node 2i?

If you want to get berried, Volumio

Bluesound interface is second to Roon, it's really really good.  Shunyata makes an upgraded power cord for the bluesound that's affordable.  Yeah sadly you have to go $1500+ for the next level

Has the $1500 to $2000 class of streamers from (say 5 years ago) fallen behind  less expensive streamers of today with regards to advancements  & improvements in technology and sound quality? Or has it been a relatively stable environment? 

Darko has a youtube review comparing bluesound, Auralic Aeries, Innous and bunch others.  He updates this list  https://darko.audio/the-darko-dac-index/

I went to the same route you are going. I am using the Allo Digione Signature with Volumio with very good results.
Darko also reviewed and compared both.
https://www.youtube.com/watch?v=tJIj0Acq99o