1. Small step, but have familiars and pets on client side only. Or if there is a public outcry of "I earned this pet to show it off" then have them only displayed in public areas.
All cosmetic things are client side as standard in programming.
Gameplay things are server side.
This means that only gameplay pets like druid wolf, wizard skeleton or summons from spells are calculated server side.
If you have 2 computers, then you can notice that cosmetic pets get random position based on character, so it can be different on each screen, which means it is not fully synchronized, but simplified for optimization reasons.
Too many visuals have potential to cause client side lag even on modern computer if engine has internal limits.
Client side lag can be reduced by lowering graphic settings.
2. Maybe auras effecting other's dice rolls need to be changed? I am just a guy with no dev or coding experience. But logically auras have to add extra to the calculations needed and take bandwidth. If Player A has an aura that effects others then A has to send the calculation to server. It has to change my outcome/stats all in the time when I swing a weapon and send that result back to everyone. Multiplied how many times in how many instances?
Every calculation adds small "brick" to lag.
Removing just auras will not noticeably improve performance since there are tons of other things that have no less impact.
3. Maybe double shots/strikes just need to roll the exact same damage number as the first hit? Same with repeaters. It seems that would reduce the calculations on the server side.
As far as I understood doublestrike/doubleshot update message, that was the intention, so they already just multiplied damage numbers instead of being separated calculation.
Repeater still gets separated proc per shot, but speed is slowed.
4. Admit that the number of active people playing slows down the servers? Do some the math necessary to see how many players need to move to the least populated server and offer incentives to make the move. Keep the population steady during prime time.
Maybe some US people could be transfered to Cormyr, but I guess they already have connections with friends that want to play with.
This still will not solve roots of lag, so if population will grow for some reason and we get more new content that add new calculations, then nothing change for better.