I do agree that it would be easier for everyone to have one and only one
member on the line relation per actual stop.
However, trains and sometimes also trams can have a significant length.
Walking the full length of a train can take as long as 7 or 8 minutes.
There are applications that send people before stepping on the train to
the right section to have a shortest possible walk after getting off
(search for e.g. "london tube exit routing", no link here to not
advertise a specific one).
We render OSM useless for such applications if we force people towards
adding fictitious nodes for trains. Please note that an easy approach
like adding a node at the front position of the train does not bail out
us because there are platforms that are called at in both directions of
travel. In such cases, also the middle position of a train may vary.
Therefore I suggest to drop the node requirement and keep up the
requirement to have only one object per stop.
A second thing for simplication: I suggest to require always a "name"
tag on the member object or multiple "name:XX" tags if there is no
preferred name in a multilingual setting. This way we could safely
ignore relations for stop related objects.
When writing both a plugin for JOSM and the display tool
it was the most frustrating part to go on a quest to find the
appplicable name if people had hidden it in some special relation,
including scores of new possible kinds of error if one has no or
multiple names from multiple stop_area relations and so on. This was the
main reason to discontinue the development.
I consider to write a proposal for the "name" requirement. Would it make
more sense for you to instead include that in your proposal, i.e. add
the requirement for the member object to have a "name" or multiple
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