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As has been stated numerous times, this is a hard fork - so go ahead, make the changes you propose, release them, fork the blockchain, and see how many people follow you to your new alt-coin.
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Not necessarily. Forced activity could easily be implemented using coin blacklisting. A blacklisting and registry authority could be completely stand-alone. Such efforts could benefit by cooperation from the Bitcoin development team, but it is not really necessary.
What would you call a situation where part of the network (miners and clients) do not subscribe to the black lists and the other part of the network (miners and clients) do subscribe to the black lists?
The part that is ignoring the black lists will allow the black listed coins to be moved to new addresses. These transactions will be put into blocks by the miners that are ignoring the black lists.
The blocks containing these black listed transactions will not be accepted by the part of the network that is a slave to the black list. They will create their own chain of blocks without the blocks containing the black listed transactions.
How can you say this is not a hard fork?
It is the definition of a hard fork.