Understood, and I’ve occasionally shared that frustration. To me it’s worth it too know that my browser cannot just take over my screen without specific permission. (I don’t know the actual permission structure here, but as I’ve never seen that behavior, I expect that it’s prohibited.)
I guess that it would be possible to add javascript to the macro to do that, but instead what you could do is create a youtube playlist beforehand, then while teaching you would enable fullscreen mode once with the youtube player button. After that you will be able to stay in fullscreen while switching from one video to another.
PS: I updated the macro, now you can chain up videos ID with a comma to create a playlist without a youtube account 
For example:
<<yt "sw9Q-iQIHMU,129w4tOuNsY,UtbekAouvWI,7gjUhl_3X10">> will produce the following embed url: https://www.youtube-nocookie.com/embed/?playlist=sw9Q-iQIHMU,129w4tOuNsY,UtbekAouvWI,7gjUhl_3X10&index=&start=0&end=&autoplay=1&cc_lang_pref=&cc_load_policy=&color=&controls=&disablekb=&fs=&hl=&iv_load_policy=3&modestbranding=1
I agree, I don’t know how chapter linking could be implemented - it would probably require using the YouTube API. And why not also use the SponsorBlock API to skip sponsors? If anyone wants to try, please feel free to post your solution here. The same goes for annotations; I don’t plan to work on this as of now, but if anyone creates their own solution, it would be great!