For this post, I will call my intentional ethnicity "EthnoX". To be a member of EthnoX:
For this post, I will call my intentional ethnicity "EthnoX". To be a member of EthnoX, either be born from two EthnoX parents or pass a test on Old Testament knowledge or on Quran knowledge and a test of Go skill. I carefully selected this criteria for membership to produce the kind of ethnicity that I would want. For programmers:
be born from two EthnoX parents OR (pass a test (on Old Testament knowledge OR on Quran knowledge) AND a test of Go skill)
An ethnicity must have shared attributes including things like genetics and culture. This is achieved by marrying within the group and so passing on attributes to the next generation. This is why it is very important to have an incentive for an EthnoX to marry another EthnoX. Most ethnicities are land-based, so they marry within the group naturally. But when an ethnicity becomes too successful and so attracts many immigrants, they have a problem. Pericles solved this for Ancient Athens by requiring that both parents are Athenian citizens for the child to be an Athenian citizen. This is the source of my idea on this. Judaism not optimimal in only requiring one parent (mother for Talmudic, father of Karaite) because this allows untested genes into the gene pool.
One other central reason for this criteria is that it selects for ethnocentrism. An ethnicity that doesn't have its own land must be strongly ethnocentric to survive. Those who are not strongly ethnocentric must leave. I think Jews have a benefited a lot by selecting for ethnocentrism. Since I am racially Jewish, I think I inherited a strong ethnocentric instinct but unfortunately there is no current ethnicity (including Jews) worthy of being ethnocentric towards. EthnoX should be a worthy ethnicity with a strongly ethnocentric population.
The other two requirements are tests for joining. The first is knowing the Old Testament or the Quran. These two books are the fundamental religious texts of western culture. Knowledge of either book shows at least willingness to learn religion, but quite possibly is a result of some commitment to religion. Why not the New Testament? Because those Christian groups that reject the Old Testament are all evil. Good Christians know the Old Testament. Why not other scriptures? Because only these scriptures produced successful cultures in the West. The Old Testament covers Christians, former Jews, and moral atheists. The Quran covers Muslims.
The second requirement is skill at the game of Go. I was a fairly good chess player and I know most traditional games of skill, and Go is by far the best. Go tests for intelligence, judgement, perseverance to build a skill, and ability to prioritize. Anyone who can play Go well has the intelligence to understand scripture. Most Muslims are an example of what happens when people who haven't developed their intelligence and perseverance try to follow a good religion (Islam), it just doesn't work. Having Go as a requirement to join EthnoX will result in EthnoX being the most intelligent ethnicity in the world.
I chose two requirements because I think this is the minimum that works. These two complement each other. I don't want stupid religious people. And I don't want intelligent people with no interest in religion. The ideal population should be intelligent and religious (the religion itself can vary).
So here I have fleshed out my fantasy for an intentional ethnicity. I am not inflexibly tied to this idea, but I want to give an example of what I am thinking about.
Essentially, the formation of an ethnicity is the long-term process of establishing large-enough commune or sect that can avoid outward influence, both culturally and genetically. The Amish are an obvious example. Serbia is another one.
"Typically people living together without too much outside influence will naturally become an ethnicity." This is the key essence and key problem for the formation of an ethnicity. I would split it into 2 aspects:
1) creation of ethnicity and
2) maintaining an ethnicity.
The creation can be assessed by having a selected group. For creating a higher ethnicity, tests as you mentioned would be essential to form a reasonable base stock.
To maintain, it would be of highest importance to make LEAVING far easier than JOINING. The concept of exclusivity needs to be an essential part of the ethnicity's self-understanding. Current religions, in particular Islam, do the exact opposite. This allowed them to grow in size, but lose in quality.