Do we still need juju upgrade-charm --switch ... ?

[Ian Booth]

So we have a feature of upgrade-charm which allows you to crossgrade to a
different charm than the one originally deployed.

>From the upgrade-charm help docs:

The new charm's URL and revision are inferred as they would be when running a
deploy command.
Please note that --switch is dangerous, because juju only has limited
information with which to determine compatibility; the operation will succeed,
regardless of potential havoc.

What is the use case for this functionality? I seemed to get the impression it
was used mainly with local repos? But given local repos are going away in 2.0,
do we still need it? And given the potential for users getting things wrong, do
we even want to keep it regardless? Note also --switch is not allowed with
--path which is how local charms are upgraded.

What would folks lose if --switch were to be dropped for 2.0? Any objections to
doing this?