Personally, I think the Ark is indeed most likely in Ethiopia, and that its return is in view of Isaiah 18. I also think that just as it represents God's throne in the tabernacle (see below) the Mercy Seat will be the throne on which the Messiah will sit after His return. That's just my speculation, however.
Thanks for the ping!
If the Ark was removed from the Kingdom of David, it probably happened when the pharaoh "Shishak" sacked the city. The Hancock version sez that Solomon's love child nonchalantly grabbed it and slid it right out of the country before anyone was onto him. And then the thief left it at Elephantine, for no apparent reason, where it stayed for (I think it was) 800 years, before it was removed to Ethiopia (again, for no apparent reason).
IOW, I think that it *isn't* in Ethiopia, unless it went there as war booty during the Ethiopian dynasty, after having been carried off by "Shishak".
There are those who think it was hidden, and that the details of its hiding place are themselves concealed in either the OT, or (according to at least one researcher) in the Copper Scroll.
IMHO, the most likely scenario is that the Ark was destroyed (the gold peeled off, the wood burned) when "Shishak" sacked Jerusalem, with a possibility that it was carried off as booty to Egypt. I don't think it was ever referenced in the Scriptures -- except in the past tense -- after "Shishak".