Note that it really doesn't make sense to talk about 'address x on the y-network' absent a change to make formerly legal addresses illegal or vice versa.  Such changes are possible and may be used as tools/weapons when the battle warms up, but that has not been discussed much and is not part of the current conversation.

Also be clear that re-playing a transaction on 'the other chain' (I would anticipate 'the other chainS' being more relevant) does not necessarily do anyone any good unless they control the keys on the recipient end of things.  It is, of course, trivial to send transactions to oneself so that both the sending and receiving keys are controlled and that will be how clued-in people 'double up'.


Yes!  That would be very wise indeed.