You will be able to spend in game cash to trigger an event but it will follow all of the parameters above. I will also probably make it so you can buy events through the donation site for $5 because why not. The whole purpose of these events is to give you something to look forward to + it will enable some competition
This system may have it's flaws, what if the event didn't run? Then you'd have to go through the trouble of refunding.
How about we repurpose the black currency coins from the evocity update and use them as "Event Tokens". If you donate money (ingame or real), you will recieve a few Event Tokens. You can use these to start events, and if they don't run, you get your token back.
You could also add these as one of the yellow (rarest) drops in unboxing.