When I type "proc" and then press C+b in PL-SQL editmode, it gets completed with "EDURE", forming the (correct) keyword "procEDURE". I know, I could type "PROC" and it would be "PROCEDURE" and if I wanted "procedure", I could change PL-SQL.xml accordingly. But why not check for the last letter typed, and add an uppercase version or an lowercase version of the substring.
Personally, I wouldn't replace the whole word with the text case used in the xml, because that would look like "parsing" (ask VB developers, they use this all the time) and then the case should also be changed for completely typed words.

Dirk