Anon…nope. we will use aidim again when we have Sanhedrin; the gemara says that openly. We use the calendar specifically because we don’t have beis din smuchim.
As for electronic forms of communication; nothing’s written in stone. The world could change, computers could all cease to exist – anything’s possible.
As for shevuos, you could have asked better – why keep the 8th day of pesach and sukkos, since the shluchim could have reached the galuyis by then?
As with your original question, the gemara openly addresses it in rosh hashanah 21a. Since we made the takanah, we are not mechalek between yomim tovim.
I have all the patience in the world for someone who doesn’t know things, be it because of their upbringing, lack of education, or learning difficulty – what i have little patience for is chutzpah. Brazenly attacking concepts that one doesn’t understand and limiting them to his tiny depth and breadth of knowledge… it’s a form of bizayon Hatorah.
If you want to know, ask. If you want to show everyone pompous ignorance, continue blasting gemaros without having learned them. I’ve yet to see you quote a single mareh makom on this forum.