Personal missions - a timed challenge

I'd love another time dependent task (like the boats and events) and I think it would add a lot to the game if we got personal missions, a bit like the events, but at a time of our choosing.

For example: a letter coukd arrive, or a hot air balloon could land, each day with a "your mission should you choose to accept it..." challenge. The personal missions would be things like sow and reap 100 tomatoes, serve 20 town visitors, catch 30 fish, catch a sockey(e) salmon, fill two boats without help, add a decoration to your farm, place 10 ads, etc etc. ...The mission would always give you an achievable but challenging time frame. The reward should be diamonds, in my opinion, but there could be new exclusive items instead/too - pinwheel decoration for example - exclusive trees - exclusive haystack - that are awarded as prizes. Like boats, you can cast off the balloon/ trash the letter if you don't want to play. And there could be an option to get a new mission using diamonds.

This is just an example to show what I mean. Hopefully something like this would be an addition for all levels, meaning the higher levels could have new things to play for even when there are no new machines to unlock.