If you're going to touch rammus in the tank update...

The only thing I would want is maybe 'taunting a minion/monster, taunts a whole area of minions/monsters'. That's all.

This will help lanemus so much without making him op. Farming has always been awkward on rammus as you need to go ahead of your wave so that you get minion aggro. you can't do that early game or when minions are pushed to your tower and so making an aoe taunt on minions will help so much. It will also give him an extra niche of being able to save towers from massive waves and would be a unique ability. This will will also help jungling as his taunt reduces mr/ar of those taunted

IMO Rammus doesn't need any more changes. He doesn't lack identity; he is the anti-ADC/yi/trynda. He wants you to fight him while saying ok. His kit also synergises so well with itself, and all his abilities are iconic. No champion can boast having both at such a high level. changing anything would make him feel not like rammus at all tbh.

PS. other minor changes that won't affect him too much: having a possible 0.05 ad scaling on ult?