I love the idea of that platform in the video, but watching him handle and move it gave me a panic attack. I imagined the metal posts banging into the glass or house walls. If I was designing a standing shelf I would use something like this heavy duty drawer slide instead:
https://www.ovisonline.com/350Mm-13...ess-Steel-Drawer-Slide-53-Mm-244Lb-P2512.aspx
I built some shelves for my canning food with a heavy duty slide like this. Those can hold 300lbs at 36" extension. I stood on one at the edge while fully extended and it was very solid. Some of them can lock when extended (that would be advisable for this application) the version I linked doesn't. But it is Stainless and marine rated. A better search could probably find one that locks. A lock would not be difficult to design if you can't find a version that locks (like add a standard barrel bolt, etc..)
I'm 6'2" and still need a step ladder sometimes. If/when I design another stand for a bigger tank I am totally doing this!