Would it be possible in autocorrect to define just the lowercase letters [ie] without any punctuation as a word to be autocorrected to [i.e.] ? If so, then the option to capitalize the first letter of a sentence might then capitalize the [I] for you…?
If that works, or doesn’t quite work, you might try creating an autocorrect where [iei] performed the autocorrect you want. Then, in use, you would intentionally mistype the trigger and get the desired result.
I haven’t played with autocorrect in Scrivener much. But in Word, I have [ie] set to autocorrect to [i.e.,] inclusive of the final comma. I have [e.g.,] set up similarly.
AutoHotKey would also be able to handle this. But AHK is usually not worth using for just one or two operations. If you do try AHK, be sure to remove all variations of ie from Scrivener’s autocorrect just so you don’t confuse either yourself or Scrivener, or AHK.
Didn’t see this reply from MM before my similar suggestion:
Yes, it should be possible to get something like that to work.