The benefits of being able to reliably and comfortably rent a pcity
room for fellow players (without giving any sort of permanent
ownership) seems to be a bit underrated, considering how beneficial
this arrangement would be specially for the newbies.

I've thought of a number of details I feel would help in this task,
but let's start with these 2 and go on from there based on feedback:

1) a welcome mat

A pcity maintainer could buy this item and drop it in a room he
owns. This would allow all players to 'start here' in this room.
The mat should also contain a list of players who are allowed to
set their starting location in order to prevent unwanted visitors
to set their starting location in private rooms.

Currently, as far as I know, setting your starting location in a
pcity room is only allowed for room owners. With a welcome mat this
restriction could be avoided.

2) A new kind of key and lock for doors

A room owner could go to a door and force its lock to be rekeyed.
[This would cause an internal variable of the lock to be shuffled.]

Then he could buy a key, take it to the door and alter the key to
match the lock [which would match the key's variable to the lock's
variable]. After this, the key could be used to lock/unlock that
door [or any other door that happens to have the same variable].

Then he could give the key to any player, who would then be able to
lock/unlock the door with the key, without any sort of ownership in
any of the rooms. Nowadays when items save in your inventory over
reboots, this feature would be feasible.

(Conceptually this is not far from how keys and locks work IRL.)

As far as I know, keys currently available in the furniture store
operate somehow based on room ownerships.

Thanks for your consideration, Faisel.