The Opt In process works as below (full guides will be produced in the near future, for when it opens):
- Pre-Launch Opt In: Anyone who opts in before snapshot will receive xym at genesis/nemesis of Symbol
- Snapshot: Balances of NIS1 will be snapshot at a specific block height
- Genesis/Nemesis: Will occur at launch and release xym to holders that opted in pre-launch, they will receive the same amount of XYM as the amount of XEM they held at snapshot
- Unclaimed Balances: Any balances of XEM at launch that were not opted in, will be held for up to 6 years to allow claims
- Post Launch Opt In: Anyone who held XEM at snapshot and didn’t opt in pre-launch, will be able to claim their tokens from the unclaimed balances for up to 6 years
To the question of whether exchange will receive them to be able to list before general distribution? (I’m paraphrasing). The exchanges will have to opt in, he same as other holders, in order to receive their XYM. Therefore they will not hold any XYM before other holders.
It is up to the individual exchanges to decide how/when/if they opt in and/or distribute any xym tokens since they will control the keys to the accounts.
The question is generally asked so people can ascertain the value of the token at time it is distributed, given the token will not have been in existence until genesis/nemesis and all holders will receive it at the same time, it seems a reasonable assertion (and is the one I will be using personally with my accountant) to say that the token was of 0 value at the time you received it. I am not a tax advisor or lawyer (and all the usual disclaimers you would expect here) and people do need to check it for their own personal circumstances and locations.