That doublesight specs out well but I wouldn't bet on the quality.
I am still using my 275t and the only monitors I've seen that stand up to these Samsung T's are the Dell Ultrasharps. I am using an Asus Proart as a secondary and it is nowhere near as nice as the Sammy, though it does run a lot cooler.
I keep thinking that 4k high framerate monitors must be just around the corner but I never hear anything about it.
The DS, HP ad Dell all use te same LG panel so differences would ave to be in extra features and build quality. When I originally saw the DoubleSight it was quite price competitive to the Dell and HP (several hundred dollars less). Of course the only prices I could find at the time were in the US but the only Canadian distributors are selling then for the same (or higher!) which drops them to the bottom of the category unless they turn out to be something special - and I can't find any formal reviews (which for the niche is odd in itself).
I agree this 275T+is a great monitor and I only wish I had gotten a 305T+.
The 30" NEC would be nice but $2000+ for a monitor is outside the budget :)
Obsolescence is just a lack of imagination.