I love the idea but this is poised to be limited only to my use. I can't get my wife and kids to do the same. Platform wins, if we're on iOS, the best calendar is the one that will sync across our events, period.
Additionally this is not a great format for recurrence, which has to be done manually, reminders(nil), notifications, change tracking (without git), location information and you're obviously at the mercy of typos.
For my use, lack synchronization with other organizations' or person's calendars is indeed a limitation with calendar.txt. Adding events manually is obviously slower than just clicking accept. Adding that feature would likely mean tradeoff for reliability, security and simplicity.
Synchronizing my own calendar.txt between my own devices has worked very well for me using git and synchthing. I also find it very easy to audit correctness of synch, thanks to plain text and version control.
For recurring events, I have found calendar.txt much easier for my use. Many recurring events have small number of events in any given year. Also, there are often exception or two, and some entries get more specific over time.
I have found adding recurring events much faster with a text editor than any of the calendar programs I've used. As the author of calendar.txt, I'm of course biased here.
Additionally this is not a great format for recurrence, which has to be done manually, reminders(nil), notifications, change tracking (without git), location information and you're obviously at the mercy of typos.