I don't see the reason that we need to keep PTS1 alive.
We don't want to keep it alive.
We want everyone to move to PTS2 as soon as possible.
But PTS lives on as long as people still mine it.
PTS is a free agent. Autonomous. No one has the power to kill it.
That said, since we are supporting PTS2, I would expect PTS to fall into disuse pretty quickly after the PTS2 snapshot.
The only reason for even discussing this is to address concerns expressed by some about the right of Invictus to offer an upgrade and what the implications of the Social Consensus are.
So, if we reach consensus this can be done easily.
If not, we have to fall back on what everybody has the right to do: release a competing chain and see if it catches on.