No reason there shouldn’t be plumbing. Heating the Mikva will be done either through microwave or infrared light, or at least not by sticking in a heated iron.
I’m sure there will be a website to pay for Kinim and to donate for the Tamid and other Shekalim. Being that the web will be cleaned up at that point it won’t be a Bezayon that the Beis Hamikdosh will have a site. No ads, though.
A big beautiful clock can stand over the Ulam.
The question is, will the Leviim use amplifiers? If yes, will they use pickups on the violin, or to preserve sound quality they won’t? What about electrical instruments? Perhaps it depends if Ikkar Shira B’Peh (if Bloomberg lets). If not, what about electronic assisted instruments (e.g. electric guitar, elec. violin, ancient elec. organs)? Also, being that there are many Karbanos at the same time we don’t want Shira cross-talk. Maybe we’ll use mutes.
Is cat gut OK for a violin in the Mikdash? Do we say Mimashke Yisroel? Does this also depend on what is Ikkar Shira?
Will the Kohanim have shwarma? Burgers?
Will we set up a Mikdash cam?