What's stopping me is that time conversion is complex and incredibly difficult to get right. In order for a format to be successful, it must be usable on all platforms big and small, and across all programming languages. The more complex the task of implementing the format, the less likely it is to be successful.
TAI conversions are not equally available or of the same quality on all platforms and technologies, whereas Gregorian time is available pretty much everywhere and is well tested, robust, and easy to use (relatively speaking. Time is never easy).
If it turns out in future that I've made a serious blunder with this policy, I could just add a new type "TAI time" and bump the Concise Encoding spec version (Concise Encoding documents all specify which version of the spec they adhere to). There are still about 30 or so RESERVED type slots in the binary spec so we're not about to run out. We then get the type, just a little late. The alternative is that I make the format needlessly complicated by pre-emptively adding TAI, and risk destroying its adoption. Being right doesn't mean success...
TAI conversions are not equally available or of the same quality on all platforms and technologies, whereas Gregorian time is available pretty much everywhere and is well tested, robust, and easy to use (relatively speaking. Time is never easy).
If it turns out in future that I've made a serious blunder with this policy, I could just add a new type "TAI time" and bump the Concise Encoding spec version (Concise Encoding documents all specify which version of the spec they adhere to). There are still about 30 or so RESERVED type slots in the binary spec so we're not about to run out. We then get the type, just a little late. The alternative is that I make the format needlessly complicated by pre-emptively adding TAI, and risk destroying its adoption. Being right doesn't mean success...