The 30 minute limit had little to do with heat:

https://www.fujirumors.com/yes-eu-import-duty-reason-fujifil...

In addition to the recording limits on a DSLR, you might need to rest it for a good while if you're filming for a long time with too much light on a hot day. It shuts off when the sensor's too hot.

Well, that's not exactly right -they're two sides of a coin. twice the pixels equals twice the power at almost every level. The pixel level, the image signal processor level, the processor, and storage.

That is a valid problem, but with MR pass through there is also a compute issue. The cameras are not in the same location as the users eyes. They have a wider parallax than the users eyes and are forward several inches. There is no simple transformation to correct the video to have the same perspective as the user. Instead a 3d representation of the environment must be created, camera imagery projected on to it, and then rendered to the position of the user’s eye. All of this done as fast as possible and highest rate possible. This explodes in compute with increasing resolutions. MQP is doing this with 3 cameras, color compositing, and without the aide of a depth camera.