It is definitely my intention to add new events to the game. I consider it almost like an expansion deck of cards for a board game. They generally don't change the core of the game but it adds variety and some unexpected interactions that can be interesting.
The unreleased official MULE sequel did both of what you propose and I definitely look at it as a sort of authority on where MULE was likely going before it got cancelled.
Moving the river valley around is not impossible but it'd take a bit of engineering because the original developers based a bit around the notion that the river is vertical line.
Moving the X coordinate of the river valley is more achievable. And it'd give the appearance of what I recall the sequel referred to as oasises.
What would be harder is having more than one river valley plot per row.
I'm a little hazy at the moment as per what all the MULE sequel's events were but what comes to mind are variants of pirates. I think added like food pirates and such--but I could just be falsely remembering this because food pirates would likely kill a game in its tracks.
I'm guessing they had working were probably just ideas and they were probably subject to change. My understanding that part of the reason the sequel got cancelled was just that theain designer was unhappy with the state of it.
I've of course have thought of my own ideas for events. Some simple but some fairly significant. For instance, I could introduce a sort of mini game (MULE has tons of those, like hunting the Wampus or playing minesweeper with the crystite) where a mule catches a virus that produces both a negative and positive outcome (to keep it balanced)--the virus would boost mules' mining ability but would hurt their ability to produce consumables. And every round after the initial virus outbreak there is a chance of the virus spreading to your other plots or your neighbors'. Maybe that's good for you, maybe not. You'd have to decide. To rid the virus you would need to take the mule back to the corral.
Your ideas are cool and I think they should be accepted as MULE like events because they seem like slight variations on existing mechanics in the game.
As per turn events, what if instead of the dreaded lost plot plots are merely exchanged between players?
I'm totally open to more ideas. I encourage people to submit and explain them. If anything it's just really fun to talk about. And if they are favored, they would more likely end up in the game. Less work for me (maybe...).
My last update to the game widened the path to introducing customization in the number of each event, which is my eventual intention. And adding that enhancement is the precursor to adding new events entirely.
Thanks for the feedback!