Someone help me fully understand this...I get that for XT to be implemented and Core forced to switch over, we must have 75% XT nodes by January 11, 2016, and it must remain above 75% for 2 weeks. If this fails to happen, will XT nodes be forced to switch back to Core, or will we indefinitely have both Core and XT nodes?
Quick ELI5:
Running XT at this time is equivalent with running Core. It's the same network, and the same Bitcoins. At some point in the future, if 75% mining majority is reached (but not before January 2016), the network will split whenever a miner creates a block larger than 1MB. This will not be accepted by Core unless they adopt a large blocks patch, but will be accepted by XT, and at this point there will effectively be two chains.
Running XT means that you will always be on the largest (75%+) chain, regardless of whether the fork actually happens or not. Running Core means that you will be left behind if a 75% majority is reached. Regardless of which version you run, coins will be safe (on both chains) as long as you acquired them prior to the fork, and for some time the chains will largely mirror each other.
So if I'm not running a node, my coins purchased pre- and post-fork (if the fork happens) will all be safe?
Yes.
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