It's very stupid to expect people to stare at system chat all day for the various things that need immediate reaction.

1) Siege timers - counts down to when the siege stone goes vulnerable, then counts down to when bindstone is vulnerable, then counts down to when siege ends.
2) Obelisk disable - once someone uses a usurper wand, everyone should have an onscreen warning of the 3 minute countdown until it can be stolen.
3) Rune glyph - 5 minute countdown after it was "sieged" and before it becomes vulnerable should be onscreen.
4) Holding taxes are due within 24 hours - active clans should never be losing their holding because they missed the single 24 hour warning in system chat.
5) House taxes - This one is currently pretty hard to miss, but why not just give an onscreen warning if you're within 24 hours of losing a house you're living in.
6) Enemy in holding - the more sophisticated clans can automate this anyway with bots, so why not just give us an onscreen warning of how many enemies are currently in system for each holding.

Not sure what your ability is to add new elements to the UI, but maybe the current "small onscreen text" that everyone just disables could be modified to suit our purposes.

Included a basic mockup of how i think it should look