Further Scripture in support of both a literal meaning, and a deeper spiritual truth.
For it is written in the Law of Moses: “Do not muzzle an ox while it is treading out the grain.” Is it about oxen that God is concerned? Surely he says this for us, doesn’t he? Yes, this was written for us, because whoever plows and threshes should be able to do so in the hope of sharing in the harvest. If we have sown spiritual seed among you, is it too much if we reap a material harvest from you? 1 Corinthians 9:9-11 NIV
So yes, no more sea could literally mean no more sea on the new earth. The fact that it is mentioned in Scripture could also mean that there is a spiritual truth being taught. Your thesis that it means we will all be one big happy family on the new earth seems reasonable. Jew and Gentile will agape each other equally, so will French, Dutch, Hutu Tutsi, etc..