Have you ever looked at "bare" latex? It really isn't any more complicated than html. Especially early html.
But you are being somewhat naïve on the render in thirty years point. Html from two years so probably renders differently today. Never mind how different it is on machine that is rendering it.
So, could someone have made a simple one? Maybe. Evidence looks unlikely. Plenty have tried.
Well, I'm not so sure if LaTeX renders the same in 30 years, given all the packages and their dependencies, that might also change. In fact, I'm not sure the document will even still compile by then.
If be surprised if latex didn't compile. Maybe people today make packages that break, buy I doubt it. The reason there are so many packages is because changes should only fix bugs. Not change current working behaviour. So bugs are typically defined as clear crashes.
But you are being somewhat naïve on the render in thirty years point. Html from two years so probably renders differently today. Never mind how different it is on machine that is rendering it.
So, could someone have made a simple one? Maybe. Evidence looks unlikely. Plenty have tried.