"8Behold, the eyes of the Lord GOD are upon the sinful kingdom, and I will destroy it from off the face of the earth; saving that I will not utterly destroy the house of Jacob, saith the LORD. 9For, lo, I will command, and I will sift the house of Israel among all nations, like as corn is sifted in a sieve, yet shall not the least grain fall upon the earth. 10All the sinners of my people shall die by the sword, which say, The evil shall not overtake nor prevent us."
Has this above all been fulfilled yet? or is it being fulfilled now and more in the future. As a matter of fact, while the house of Israel is being sifted through the nations, God is visiting those nations to take out of them a people for his name, just as James said. And "after this" includes both the sifting of Israel through the nations as well as the taking out of those Gentile nations a people for his name. They have been going on simultaneously for centuries.
Furthermore James may be quoting just Amos here, but he is acknowledging that he did his homework and read all the prophets from Isaiah to Jeremiah to Ezekiel to Zechariah to Malachi ..., and they all prophesied that what Peter said was happening to the Gentiles would happen and would continue to happen until it was finally finished, then He would return.
Not just Amos but all the prophets were in agreement with what James and Peter said, prophets like Isaiah:
"For the Lord will have mercy on Jacob, and will yet choose Israel, and set them in their own land, and the sojourners shall be joined with them and they shall cling to the house of Jacob".
And Zechariah: "I will dwell in the midst of thee [O daughter of Zion]. And many nations shall be joined to the Lord in that day, and shall be my people ... and the Lord shall inherit Judah as his portion in the holy land, and choose Jerusalem again".
And Amos: " 11In that day will I raise up the tabernacle of David that is fallen, and close up the breaches thereof; and I will raise up his ruins, and I will build it as in the days of old: 12That they may possess the remnant of Edom [should be men not Edom], and of all the heathen, which are called by my name, saith the LORD that doeth this. 13Behold, the days come, saith the LORD, that the plowman shall overtake the reaper, and the treader of grapes him that soweth seed; and the mountains shall drop sweet wine, and all the hills shall melt. 14And I will bring again the captivity of my people of Israel, and they shall build the waste cities, and inhabit them; and they shall plant vineyards, and drink the wine thereof; they shall also make gardens, and eat the fruit of them. 15And I will plant them upon their land, and they shall no more be pulled up out of their land which I have given them, saith the LORD thy God."
Unless something has changed since the last time I posted on this to you, they still occur after.
Has this above all been fulfilled yet?
Jeremiah and Ezekiel certainly thought so. So did James.
However, I have learned from talking with people sometimes that we should expect a retort of "well, kinda... but the REAL fulfillment is ...." and we are off to a land of charts. The problem is that THE TEXT SAYS that this (the Acts 15 events of the Gentiles coming to faith) is the fulfillment of the passage in Amos 9:11ff.
The rest of your post deals with other pericopes of scripture, which I would happily discuss with you at another time.
Back to the original point. You pointed that Acts 15 was a lynchpin in support of the dispensations. My contention is that it is NOT, but is rather a refutation of the very guts of the dispensational hermeneutic, as we have a clear and unambiguous statement by the Holy Spirit through the mouth of James that there is a SPIRITUAL fulfillment of a literal promise. This is, again, the clear and common sense reading of the passage, and that is why before the rise of Darbyism that ALL the earlier church fathers (reformed, and non-reformed, as I mentioned John Wesley earlier, but left out the Catholic fathers, as I didn't figure you would put much stock in their writings) viewed it as a simple figurative (or "allegorical" if you prefer) fulfillment of the prophecy. So do I. So did the whole church before some Irvingite charismatic milkmaid helped the whole church to see that their hermeneutic in interpreting OT prophecy had been wrong for 1800 years.