Some really basic concepts weren't even realized back then one big one is hypertext - its not really a complex thing when you think about it but undiscovered then.

At the time many folks were graduating from cassette/paper tape to floppy disk, so random text file usage was kind of a new thing to many micro owners, text files were there but mainly used to store program variable data. Other concepts like compression, graphics formats, remote updating, distributed data, etc. were in their infancy.

I would think someone going back there would have an advantage, they may have to learn the old languages then build a whole lot of tools, but they would know more advanced end results which is a lot better then trial and error to reach those points originally.