R E T I N A. Still waiting in 2024. Surreal.

Here in this thread you will finde the answer to that question from the CPO of NI:

Making Traktor high-res requires us to rebuild the whole Traktor app in a new UI framework. We had to make a tradeoff last year between doing that, and releasing the features we added in Pro 4 (Stems, flexi beatgrids, pattern player, Ozone maximiser) — Feedback from our users was they'd rather have those features first, rather than a high-res UI and no new features. We plan to have high-res UI in the next major version.

If the issue is with small text, you could just lower the resolution in traktor, this may also scale better too. If the problem is blurriness and experimenting with different resolutions and dpi settings doesn't help then your stuck until NI bring proper support for very hi resolutions. Also if blurriness is the problem, that's just down to bad scaling by the OS, gpu or monitor there's absolutely no reason traktor can't be cleanly upscaled to high res without blurring.

TP4 looks excellent at 1080 on a 1440 240p 17 inch laptop upscaled to 1440 by windows, when I connect to my 4k 60p 27inch monitor it still looks great at 1080 upscaled to 4k by the monitors own scaler, I've also tested scaling via Nvidia control panel, they all scale perfectly tbh. Unless you have a monitor in excess of 27-30 inches at arms length you really don't need or even benefit much from higher resolution than 1080, your just putting more load on your gpu and potentially slowing down traktor itself, just because you have 4k doesn't mean it's of overall benefit to use it, that 4k is more for film, video games and graphical work. Dj software like all music production software, needs to prioritise performance.