Thanks for all of your votes and comments on this suggestion.
Unfortunately, this suggestion isn't currently on our roadmap. We do though understand the value in retaining custom event types during imports, and and will consider this suggestion at a later date.
For those of you who aren’t aware, in our Team Calendars 5.5 and 6.0 releases we brought a range of new improvements, including a fresh new look and feel, better event frequency options, and CalDAV – the ability to use Team Calendars in your favourite calendar app. For more information on these improvements, see: 5.5 release notes, and 6.0 release notes.
Jenny | Confluence Server Product Manager