We have coins commemorating all the occasions now.
Historically coins reflected a major national milestone or achievement but now due to surge in coin collector demand and higher profit margin led Mint’s all over the globe to make coin of less important milestone and sometimes even no milestone.
Same like stamps which comes every month commemorating so many occasions and milestones, Mint’s has also followed same path where one ounce of silver of rough value of AUD 21 stamped with national identity and packaged in a nice box can sell for $150 and sometimes run out of stock in a day or so. Since there is surge in demand, supply has to meet it and for some countries this has become a major source of income. If you check coins from a nation called Niue over the internet you will see they have coins for all the occasions ranging from Happy Birthday to Mickey Mouse to Royal Wedding etc and launched Brexit celebrating coin before even UK thought of it.
In the times when coins were casted they depicted important events in symbols and hence symbolises the rules of an authority but now with new metal stamping technique in place the coins has left symbolism somewhere and reflects jpeg picture on metal with exact colours of a picture on a coin. I saw the commemorative coin of Royal Wedding having same picture as the stamp and sold in a set.
Coins needs to scare in numbers to be collected with enthusiasm and to retains the value, moreover needs to depicts the number rather than simply having an image on them like a stamp.