It's confusingly presented in the video, but they already work in the near infrared, up to ~900nm. They're used with IR illuminators and lasers all the time.

There are tubes that work on a wider spectrum, like the Photonis 4G tubes from UV to IR 350-1100nm. But I found them dimmer than the L3Harris in the video.

Infrared is a wide range. Ambient temperature black body radiation (LWIR) is typically detected between 7..14um. Refractive optics that works from there to visible range (380..700nm) is to my knowledge still unsolved problem.

Image intensifier tubes don't care what color the incoming photons carry. Anything within reasonable wavelength/voltage/frequency that can pass and focus on input side of IIT triggers secondary electron release events, a la armor piercing shell causing spalling on an armor plate. Then the released electron hits exit side charged at high voltage and excites good old green or white phosphor paint. Frequency of that release events converts to light intensity on the screen and the user observes it through eyepiece optics.

Standard photomultipliers are single pixel vacuum tube, nightvision IIT devices are hex array of pixels. They are built on microchannel plate technology; a bundle of optical fiber, twisted, impregnated in glass into a sushi roll, silced angled, etched, electroplated, stacked, to create a circular glass plate filled with couple layers of microscopic conical voids, each working to same effect as multi-stage PMTs when charged.

I suppose, in theory, all lights from long-wave IR to X-rays can be all handled by a single IIT tube, but in reality they can't, and thermal cameras that resolves heat images works in a completely different principle; instead of using vacuum tube technology that excite on incoming photons, they receive microscopic changes in temperatures caused by incoming light focused by IR-transparent lenses, projected onto an array of individual heat sensor devices(microbolometers) that are MEMS fabricated on top of typically Sony CMOS sensors.

Combining an IIT with a CMOS camera should be possible and I guess will improve contrast/minimum light level necessary, but the tube already sees near IR that it reasonably can, and also, because the light at the exit/user side of IIT is just luminescence from phosphor, adding heat-sensitive detectors there won't yield much.

IMO, if you just want to maybe buy and use an NVG, videos from (rich/financially irresponsible)gun people such as Hop(Hoplopfheil) or InRangeTV are more brief and potentially useful. Anything beyond, I found on Google(pre-covid).

1: https://www.youtube.com/watch?v=sHflvwNJ3cs

2: https://www.youtube.com/watch?v=F3KftiMHYVU