It is of course possible, likely even that two variants of a syntax would diverge over time. At some point there will be a decision that future versions of the format will use only one of the syntaxes.
The happened in the XML world, at the start most specifications included both the DTD and XML Schema definitions of the schema. Now we only use the XML Schema version and DTDs are obsolete.
Given the way that calendar applications behave, an incompatible format change would be no bad thing. In particular, calendar applications seem to have no idea that there is a difference between local time and UTC or that daylight savings rules vary with place. I don't know if there is also a problem in the iCal format, but the applications are certainly broken.
I suspect that the problem here is the type of fourth rate 'usability' specialists who have ruined a lot of security protocols by removing information that the user needs from the user interface. They think that user acceptance scores in 60 minute lab experiments are definitive. But all that a short interaction in a lab can show you is the usability of the application for the task you give them.
Without the ability to specify the local time when setting a recurring appointment, a calendar application is broken. A meeting that happens at 9am Eastern time every week is not the same as one that happens at 2pm UK time.
When I was using Outlook it would let me specify the place I was in but didn't bother to change the time zone for me unless I did it manually and the setting would then affect the whole machine (which of course is a privileged operation). So when setting up a trip to the West cost for next week, Outlook was still trying to find me meeting times in the wrong time zone.
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