Yes, it is quite the mystery! At least I couldn't find anything. That won't stop me speculating though. :)

Searching indicates the (now dormant) Petruchio was the driving force behind changing the Perl Monks levels:

• A Proposal for Additional Levels by Petruchio (Oct 25, 2004)
• A Level Playing Field by Petruchio (Oct 31, 2005)
• Voting/Experience System (doco of current system)
• Levels of Monks (update: more doco of current system)

As you can see, all 28 of Petruchio's levels of 2005 remain intact, with just one minor tweak, Petruchio's level 28 (Pope, 100,000+) being split into two:

• Level 28, Patriarch (100,000+)
• Level 29, His Eminence (1,000,000+)

Why? I have no idea, but after examining the early history of the Perl Monks experience system, I cannot restrain myself from speculating. It seems that vroom gave himself a gift of one million XP as a reward for founding this site (to balance the books, Perl Monk antivroom was created with an XP in excess of minus one million! :).

So, and this is just a guess, perhaps the "His Eminence" level of 1,000,000+ XP was created for vroom, and vroom alone, designed to be unreachable by other monks ... though it seems we now need more (attainable) 100,000+ levels given we have three monks above 100,000 XP with nothing more to realistically strive for.