I think if you have been subdued as a result of PVP you should until the server resets have some kind of penalties to saves, ab and ability scores and spell failuire and have your movement speed decreased. To reflect the psychological and physical trauma that comes with having survived being beaten within an inch of your life.
It is just silly that a person after having survived a traumautic near death experience/shake down is able to be in a fighting mood again. I feel like these penalties would give some time and encouragement of some good psychological roleplay. It also serves a hinderance to the lame practice of going "I am in tip top mood to fight again after my ass got handed to me!" and even might make some people more willing to flee a pvp conflict going south.
People use subdual mode for duelling, this would hinder that aspect of it.
If it forced your rest timer to be reset to require another 3 or 4 hours until next rest, that could be an easy way to enforce a recovery time delay so spell users don't renew their spells instantly, or anyone in general doesn't recover their HP unless spells & potions are used.
There's also already a penalty applied to people that are subdued that represents what you suggest, but players need to act according to the situation, the low duration of it is a trust and a gentle reminder without being too harsh that players need to roleplay these injuries.
Perhaps increase that timer but have it set to your con? Higher con = faster recovery
That way it can be crueller to little hins or wizards
You can use sparring for dueling, just putting that out there.