Timestamps in Tangle are already mandatory and must have a value in a certain range, which seems to be between the last snapshot time (epoch 1517180400, which is GMT: Sunday, January 28, 2018 11:00:00 PM) and 2 hours in the future relative to the node's clock. Is this node's clock a physical clock or logical clock? If physical clock, does tangle really needs to use physical clocks for their timestamping mechanism? The fact that timestamping by nodes can be lied or mistaken by wrong physical clock, will logical clock helps?
Timestamps in transactions are from physical clock. The protocol don't relies on it except for rejecting transactions issued by an node that is largely not sync (i.e. wrong physical clock)
Timestamps are necessary. That is correct. They are included in the bundle hash. But it is not mandatory to have a correct timestamp. So, you can also set it to zero.