Is it a viable idea to start a fee-based live video instruction website?

An acquaintance of mine works full time doing 1-on-1 video instruction for a very small niche topic.

If an individual can succeed with that business model, even after reinventing every wheel, and do well enough to give up an engineer's salary, then surely a broader platform could succeed. Economies of scale should save individual instructors time, energy, and money as far as marketing and infrastructure are concerned.

Just depends on implementation ...

You mention a variety of different ideas here that although tie in to your main concept, are all over the place. I think that in order for you to understand wether it is feasible or not you will have to narrow down your concept. What I advise you to do is to write your concept down as if you are explaining it to a five year old. If you can do that then you know what you want and from there you can analyze wether it is feasible or not. But as you said if two major corporations have tried it and quit then there must be a reason for that (e.g: Too much capital required vs too little potential profit).

As a YouTube channel host, University Professor and Consultant, I applaud your enthusiasm and your caution. Good to have both at the onset!

The question that needs answering is : what subject(s) will people pay for?

Your competition is at a variety of levels : basic k-12 is covered by Khan Academy and the like. More advanced how to videos are available for free on YouTube. True - you are going for an interactive full service approach, but there are discussion boards to supplement that.

Thus, our niche platform is those subject areas or problems that must be tackled with a live guided and interactive instruction.

We can talk further about iteration, pedagogy or teaching best practices and creating an MVP for funding.
Happy to help you further, let's talk!

You could use either Uscreen or Vidello.

We produced a video for Vidello that you can view here:
https://www.vidico.com