Maybe use Matrix room upgrade mechanism to get rid of duplicate rooms

[ulope]

Problem Definition

Related to #3387

To support room version upgrades Matrix has implemented a mechanism ('tombstones') that allows informing clients that a room has been replaced by another one (spec, Synapse implementation).

Investigate if this could be useful to 'redirect' clients in case multiple rooms for a channel exist.

[ulope]

Talked with Matthew from Matrix about this. Currently the upgrade mechanism is not intended for anything but to upgrade room versions (and also probably can't be abused by 'upgrading' to the same version).

They will think about a way to merge rooms after the 1.0 release is out (scheduled for March)

[ulope]

We no longer have public rooms.