There was a game, a game I do not remember, but a game that if you do not eject from your mech before it is destroyed, your character's save files are completely removed, and you have to start from scratch.
Now, as it may seem, it may sound appealing for you all to do such things. But remember this, and remember well, that a LOT of the weapons you use are usually either only grabbable once or twice, or is extremely hard to obtain, VIA either form Enemies or Purchasement. What would happen if you lost your Dark Armor, which you can only obtain once in a playthrough (and if covenants connect from NG to NG+'s, the probably forever). You would lose your precious Katanas, unless you are part of the Forest Covenant, but even then the weapons are expensive to purchase. You will not be so eager to buy the armors you purchase from the Zena Merchant, and you would not be so hasty to try to make a character build to surround something such as a Dragon Greatsword, a Black Knight Great Axe, a Demon's Great Hammer, or other such things.
Of all the things, do you think that both invader and host would agree to such terms, to lose everything they hold? I would wager that the Invader would use internet cords, so they can easily just eject their connection to save them from death. As well, the host would do the same. Only those brave, honorable fools would fight, mostly the hosts, and they would lose everything, as those who Invade are beings who set themselves for the desire to KILL. Chew on that for a while. It sounds tempting, but the Host and Invader would not be so eager to be in such duels, rather trying to do more basic combat. Only the small, very small few would be doing so, and that quantity will be even less than the princess' guard, which I guarantee is the lowest quantity of players that are in that covenant, out of all nine. Their are even more Dragonoids than Guardians. Just saying. The invaders who hone such rings or helms would usually not be interested in honourable combat, rather combat to kill those foolish enough to think such honours exist.
As well, such weapons as the weapons enhanced to lightning weaponry will be more seen than physical, as the outcome for such weapons would be much cheaper and efficient than other builds. I Like the idea, I truly do, but the favour of a ring or helm of both sides, or even one, seems not enough... too broad. Something else would need to come into play. Something more agreeable, more stationary. A Covenant, which sins those who quit out of invasions and quits when invaded, a Covenant that focuses on Combating those of the same Covenant, a Covenant that focuses on the way of combat, in which both sides will be locked into the same positive and negative aspects. A ring and helm would seemingly hinder those to combat each other, as many depend on two rings and even the helm. No... a Covenant would be more suffice than so. A covenant that allows everything to be lost. Few will join, few of those joined will probably would be not honourable... but the rewards of such battles should be greater than those of others. Yes... that would be much greater than so.