The display frame has plenty of space for a phone-type camera sensor of any resolution, it's just a flat CMOS. Even a really big phone sensor is only 8x6x3mm
A good lens is more difficult to fit in the Z-dimension but that doesn't constrain the resolution of the sensor. A small bump in the bezel and a corresponding recess in the base would allow a better design of lens.
3mm? Based on my measurement just now, the lid of my 16" MBP is just about 4mm thick - so no, after the case and front glass there's enough room for even the sensor, let alone a lens.
Yes exactly, there's plenty of space for a decent sensor and lens. On top of that we're talking about a wide-angle lens, which are generally flatter. Two things add thickness and complexity to camera lenses - telephoto and autofocus. Phones only recently started getting thick bumps for the rear camera when telephoto lenses became more popular. My phone has a sizeable bump for the telephoto camera but the ultra-wide angle one is outside of that bump.
A good lens is more difficult to fit in the Z-dimension but that doesn't constrain the resolution of the sensor. A small bump in the bezel and a corresponding recess in the base would allow a better design of lens.