[2020] Will I get a stable 144fps once the multicore update to NXT is released?

It's hard to say based on your settings whether you would be CPU or GPU bottlenecked - I would imagine CPU bottleneck but not got first hand experience with that hardware

If you can verify that you are CPU bottlenecked (a single thread maxxed out and/or GPU usage significantly under 100%), then probably yes

You could probably go a long way to improving that by reducing the anti-aliasing quality - ultra is 8x MSAA, try medium (4x)

There is already multithreading in many areas of the game (loading, animation, audio, particles, picking, irradiance, shader compilation, the list goes on...), this change I am talking about is specifically rendering, and it is splitting it into one additional thread, as this is as far as it is possible to go in OpenGL

In an ideal case this would result in 2x maxxed our threads, in reality usually more like a 100% and a 75% (ignoring the other low load threads), with the order (ie main or render thread bottleneck) dependent on settings and quality of OpenGL driver

Well the theoretical max increase is 2x fps, you'd be doing very well to hit that, but you should see an improvement