Not sure… it might sound like a good way to prevent some alliances becoming “invincible”, but if you can’t beat a strong base, it doesn’t help you if it gives more skulls, and also it’d be another mechanic that punishes success.
You fought hard and successfully gained fiefdoms? Let’s punish you for your hard work, and give all of your enemies a bonus! Already now, the efforts needed to win a way is often by far higher than the reward, making it sometimes the better choice to lose a war. If we further punish success in wars, then why still have them?
The fact that the skulls a base offers depends only on the king’s level, and is completely independent of the base itself (meaning a lvl 100 king with maxed out and max-boosted base gives exactly as many skulls as a lvl 100 king with a completely empty, straight-path open base) is widely known. Thus, trying to “improve” the skull algorithm by including the level of certain boosts that an alliance has, while still ignoring the whole actual base itself, are most likely going to fail, as they’re reaching too short.
Also, for those alliances with horribly unfair matches (alliances with over a dozen additional or less members on your map), this whole thing wouldn’t help at all: Everyone (except the top few dozen alliances, for whatever stupid reason) get matched by fiefdoms, thus the opponents on your war map will have just as much fiefdoms as you have (give or take 1 maybe), so their skulls will be increased as much as yours. Then, why have it if it doesn’t change a thing? When I get additional skulls but my enemy gets the exact same gain from me, then what use it it?