Cannot completely add a new profile field type

There is no way to insert potentially required code in adm/style/acp_profile.html STEP 1 (lines 106 to 128) as code is hardcoded for the existing types. Given the way profilefields work, using an event would be (in my opinion) a bad resolution to this.

A flexible schema, similar to the one used for STEP 2 (lines 141 to 146), should be used.
This would require some rewriting of the profilefields/type subsystem, including additions to type_interface and all profilefields/type/* classes.