Ok, bear with me, as I suspect most people's initial reaction will be one of mild horror.
The proposal is simple: For all alliance support sent, only 10% will actually fight (and bear losses, so if you send 10k and 30% troops are lost in the fight, you'll lose 300 of the 1000 that actually fought). All troops moved around by the defender in question obviously all fight.
The reasoning is less simple.
Improved target selection
At the moment, notable on the UK server but I suspect an issue elsewhere, is that all the top alliances are now close to invulnerable (aside from ninja hits at 4am with 3k+ horrors from point blank). With a 15 minute horn 100k support is commonplace, and it only stops there because "why send more?". Not only do they have a larger % of players online than the smaller alliances, they also can quite happily hold 10k defs per castle, so only a few of them need to be able to reach the attacked player, sending from a single outpost, to break the 100k support mark.
As a result, most of the big players don't bother hitting the big alliances all that much other than to kill off excess troops, as there's no other point to doing it. Instead, it's the tier 2 and 3 alliances that get to enjoy the big 6 wave hits. It's not uncommon at the 20 million might mark to have only 2 people online in the early hours, and 9 online at peak times. Quite a few don't have level 3 stables, and a typical castle might have 2-3k defs in, which gets insta-shredded by serious hits.
Rebalancing CY fights
Obviously it's a war game, and hitting other players is a thing even if they have no hope of defending, but I know a lot of bigger players are feeling like the game has become more and more unbalanced in the direction of the defender (and this of course was one of the reasons that the outcry about the new cast was so strong -- it's already too easy to defend as it is).
3k of horrors with a breach wants to see fights against 10-15k defs, not 50-100k. By limiting alliance support to 10% of what's sent, attacks against anyone becomes somewhat plausible, and scraps for bragging rights or honour (for those who care about it anyway) against top players start to be worth having a shot at. Mid strength alliances who get a castle trashed at 4am and know that the only thing a retaliation could ever achieve is losing all their attackers for 3-4k defs split over an alliance on the other end, suddenly get the opportunity to at least seriously hit their attacker's def numbers somewhere.
Not that anyone ever uses shells or carries dead accounts for any reason or anything, but it would make the theoretical practice a lot less effective too
PvP at a high level is mostly dead other than proper wars. Single or double attacks against a 50m+ alliance at sensible o'clock is mostly an exercise in futility. Castellan and commander kits are all well and good, but it's all irrelevant against six figures of defenders. Bringing serious PvP back requires some form of counter to the massive food/troop creep that granaries/food items and everything else has brought into the game.
Alternative proposals to deal with it are just as welcome as responses to this one