That's something i would prefer rather than stats buffs. I didn't put it in the "report a bug" section because it doesn't have to do with pbe only bugs, that's why it feels more like a feedback area.
Currently there are different ways a tentacle delays or cancels its attacks.
1. Tentacles should automatically attack a vessel or spirit the moment they spawn. However if you use W just before it spawns the attack gets delayed for 1 second or even cancelled if the 12 seconds vessel time finishes during this delay.
2. If a vessel becomes a vessel near a dormant tentacle, that tentacle won't attack the vessel once it wakes up.
3. From the last buffixes, her W was made so hitting a dead or untargetable enemy would still trigger tentacle attacks. The untargetable part however only happens with close-W. If Illaoi dash w-s on an untargetable enemy tentacle attacks won't trigger.
4. Some strange W interactions happen with parries. Some parries block tentacle triggers, some others however don't. Jax parries both close w and dash w triggers. Pantheon and Shen only block dash range, they don't block the close w tentacle trigger. A strange thing also happens with teemo which blocks close w, but doesn't block dash w at all. The dash w deals the damage and also trigger the tentacle attacks.
5. Commanding the tentacle to attack twice just before the R buff finishes will delay the second attack.
6. Their agro range is based on the target's center while their attack is based on the target's edge. What this means is that even if the target is in the tentacle's attack range, that tentacle won't attack him until the target's center gets into range. This is particularly visible with chogath since his center is futher away from his edge.
Some other things.
1. Using W both triggers bone plating and deals reduced damage from it from one attack. This reduces Illaoi's poke.
2. After using W , tentacles will not put any stacks of electrocute / phase rush on the target. A strange interaction also happens when triggering conqueror with W. The following tentacles that attack won't deal any true damage or benefit from the bonus ad. Only the second tentacle attack benefits from the bonus ad while still not benefitting from the true damage. They should always benefit from the true damage and bonus ad.
3. R should buff tentacles to attack 50% faster. If however a tentacle attacks just after a te tacle finished its attack it will take the same amount of time as it did with a non-buffed tentacle. I.e Tentacles usually take 1 second for an attack. When buffed it takes 0.5 seconds. Two non-buffed tentacle attacks take 2 seconds. Two buffed take 1.5 seconds. Do the math.