Im sorry as im sure this is answered but the more I read, the more confused I get with terms about splitting and replay tx's etc.
Can somebody help me understand the specific point of holding 1 btc and then having 1 btc and 1 btc2x after fork?
There really isn't any "point" to it per se... some people don't like how BTC is now, and they want to "improve it". So they're implementing some changes and forking off... essentially, this will create an altcoin... it's possible, the new fork could become the stronger coin with more support in which case, BTC as it is now would like be considered the altcoin, and the new fork as "Bitcoin".
But what I dont get is where the 1 btc2x is generated from? Its not a new coin so its not pre-mined, right?
Basically, they just copy the current Bitcoin chain up until Block X, then split off... magically creating copies of all existing BTC. You basically double the number of coins you have. NOTE: not necessarily double the value... just double the total number.... so if you had 1 btc, you end up with 2 coins (1 btc, 1 2x)
Is it basically down to me choosing to spend either the 1 btc or the 1 btc2x but not having ability to spend both of them? This would seem to explain alot of the holes I think i have in my understanding.
No. You can definitely spend both.
After the fork, dont they have to become two seperate chains moving forward thus becoming a new altcoin? Or am I missing something here that somehow wont turn btc2x and btc into 2 chains with 2 coin types after the fork happens? Miners will be generating rewards on two chains causing generation of new coins on a new chain so i dont see how it would not be an altcoin after the fork occurs.
Yes... definitely 2 chains. It's a hard fork, they're changing the consensus rules. So we end up with two coins... Now, the real question is... which one will end up being considered the "altcoin"?
Is there a huge money risk here for a long-term btc holder that doesnt intend to stop holding? I think the answer is no, not any more than usual volatile/high-risk of cryptocurrency. Am I correct that I dont need to make a decision on my favored fork if Im just a long-term holder? If some of my above understanding is right about the 1:1 coin holding then i think I simply would hold all my btc / btc2x and in 20 years, i could cashout one or the other from my 1 coin example (but not both). Theres no decision timeline I need to worry about, right?
Well that depends... there are sort of three scenarios:
1. Bitcoin remains Bitcoin. 2X fails to get support and starts to die. In this scenario the value of the 2X coins will plummet as everyone dumps to get whatever they can before the coin becomes completely worthless.
2. 2X takes over as main "Bitcoin". Bitcoin support fades away and starts to die. In this scenario the value of Bitcoin will surely dump faster than scam ICO. You'll only have limited time to assess what is going on before you BTC is worthless.
3. Bitcoin and 2X both continue on with enough support to continue (a bit like Bitcoin Cash has done). The values will go up and down as speculators start guessing which coin is going to win, before things settle down and the world carries on as "normal"
If you really don't care, you can just hold both coins forever... and again, you CAN sell both.