My advice with wide gamut would be to avoid it unless he specifically needs to work with wide gamut content. It's only good if he has supporting content and images and a colour managed workflow. If not, you will actually find a wide gamut screen to be more complicated to work with and probably make matters worse. Not to mention paying a lot more for the privilege of it as a feature. Only reason I asked was in case that was a specific requirement but it doesn't sound like it is.
Another feature common in high end screens that you pay a premium for is 10-bit colour depth support. But to take advantage of that you need a full 10-bit end to end workflow which is expensive and tricky to achieve, and rare in fact. So again, if he specifically had all the necessary components and wanted it, that would have been something to look for, but I don't think that will be a requirement.
Another feature of higher end screens would be support for hardware calibration. You'd need an additional hardware calibration device for that, and those screens with support of that feature are the ones that tend to be high end professional grade screens. He might want to consider a calibration tool anyway, no matter what screen he goes for. Some screens will allow high levels of control and calibration of the monitor themselves, but if not, even normal screens benefit from calibration done at the graphics card level using those tools
To give you an idea, some semi pro type screens would be something like the Dell U2413 or U2713H. Those are the more lower cost range but with those high end features. More serious pro grade screens are available from Eizo and NEC as two key manufacturers so maybe have a look at this range
I expect those features are not needed from what you've said so far, and actually he'd be just as well off with a decent mainstream model like the U2515H.