D&C 84

As the Lord prophesied that a temple would be build in Zion in this generation (there are many ways that one can define generation), He also stated -

:,,,they shall remain under this condemnation until they repent and remember the new covenant, even the Book of Mormon and the former commandments which I have given them, not only to say, but to do according to that which I have written—
58 That they may bring forth fruit meet for their Father's kingdom; otherwise there remaineth a scourge and judgment to be poured out upon the children of Zion."  (Doctrine and Covenants | Section 84:57 - 58)

The fact that many would not live the law of consecration as covenanted, would in itself void any promised blessing.

The Lord also spoke of the sign -

"And the tongue of the dumb shall speak..."  (Doctrine and Covenants | Section 84:70)

In my mind, this sign has been demonstrated in my own calling.  Where I was petrified and unskillful in speaking in the beginning, the Holy Ghost as assisted me greatly in my speaking.

Finally another thought.  Speaking of supporting and sustaining missionaries, the promised -

"And he who feeds you, or clothes you, or gives you money, shall in nowise lose his reward."  Doctrine and Covenants | Section 84:90)

I believe this holds for all members that support missionaries, whether of their own family or not.