That would be an input VPN... perhaps useful if DPI was breaking user's tor access protocols (to bridges or regular entry guards), but not their VPN traffic.
Output VPN's could also be useful to allow tor users to bind their stack to it over tor, thus permitting UDP back and forth from clearnet... typical with voice video comms and a bunch of other applications that have been disabled for tor users becase tor only supports TCP.
Operators would have to publish their VPN node info somewhere for users to use... or getbridges, getvpns.
There are prior exploratory threads on this here before.
Operators can also be running and supporting VPNGate.net service as both input and output.
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