When talking about the mitzva of building the Beit Hamikdash, who has not jokingly wondered what would be if we would succeed in building the Mikdash today, just as we do about the coming of Mashiach? I have joked, and have heard many other do so as well similarly.

If Mashiach were to come, would he be Sephardi, Ashkenazi? Hassidic? Gur, Belz or Vizshnitz, or something else? If he will be Sephardi, the Ashkenazim won't follow. If Ashkenaz, the Sephardim won't. If Hassidic, nobody else will, but also within hasidism, it depends which group he is from.
Then there is the Beit Hamikdash. What hechsher will the korbanot be? Will they be glatt? Beit Yosef? Eida? Rabbanut? Hassidic hechsher? Will the kohen gadol be.... yadda yadda yadda..

you get the point..

It is no longer just a layman's joke.. The Tolna Rebbe has now said why the only way for us to get the Beit Hamikdash will be for it to fall from Heaven complete and intact, instead of being built by humans.

If you can understand the Yiddish, listen to it yourself below. If you are like me and don't know Yiddish.. here is a transcript, courtesy of Bechadrei and VIN..

“My sons, Hakadosh Baruch Hu knows his yidden.  Imagine for yourselves that Moshiach is coming.  Let’s try to picture for ourselves that we are standing now on a Motzei Shabbos and we all hear the sound of the shofar. Moshiach is here.
“The first thing that we need to do is to rebuild the Bais Hamikdash.  We all know how the chareidi world operates, Baruch Hashem.  Picture for yourselves how this Bais Hamikdash will be built.  Let me tell you what is going to happen.
“The first ones who will enter the picture will be Agudas Yisroel who will say ‘Of course we are the ones who will build the Bais Hamikdash.  We are the ones who worry about all the needs of the chareidi community. Is there any doubt that we should be the ones in charge?’  They will convene a whole assembly of gedolim in order to decide what needs to be done.
“Meanwhile, R’ Meir Porush will come and say, ‘And what about me?  The Agudah represents everyone?  I want this to be under my auspices.’  And then there will be a second group of Rabbonim discussing how to build the Bais Hamikdash.
“The Litvaks will come next and they will start to scream. ‘Gevald! The chasidism should build the Bais Hamikdash?  They will all be dancing because they don’t know anything about the actual halachos of building the Bais Hamikdash.  They will offer to find one Kohein who actually knows the halachos of the avoda. But they will tell us:  “for this part, you are going to need the Kollel Chazon Ish.  For that part you are going to need the avreichim in Brisk.”  What are you, crazy?  We will build the Bais Hamikdash.’
“Then will come Satmar, from both sides, and they will say, ‘You are all Zionists!  You are unfit to build the Bais Hamikdash.’
“The Chabadniks will also get involved.  ‘You are all crazy!  Moshiach is ours!  It is our Rebbe, our Moshiach, what are you talking about the Bais Hamikdash?  You are all insane.’
“You understand that Moshiach will come and, nebuch, it will be another long galus just until we can all agree who will build the Bais Hamikdash.
Therefore, Hakadosh Baruch Hu has made the decision for us saying, ‘Listen to me, my children. It is enough for me that you will come to the Bais Hamikdash.  I will build it on my own, because there is no other way the Bais Hamikdash could ever be built.’”