An update on this...
So I did as the email said, filled out the Exemption form along with my Photo page and a cover letter and sent it off to PennDOT last week.
I got an email reply today:
Since you have been living in London for several years, there is a question regarding your residency. Pennsylvania law only allows for the issuance of a photo exempt driver’s license to a resident of the Commonwealth; Act 152 of 2002 prohibits PennDOT from issuing or renewing driver license products for any person who is not a resident of the Commonwealth.
Please submit two proofs of Pennsylvania residency. Acceptable proof may be the most current state or federal income tax record, most current personal or property tax notice, or a recent utility bill in your name with a Pennsylvania service address. A cell phone bill, bank statement or a safety deposit bill will not be accepted.
If you cannot provide proof of residency, you may submit a written request for a refund of your renewal fee (form MV-700). You are welcome to reapply when you return to PA and can establish residence. You are welcome to reapply when you return to PA and can establish residence.
If you cannot comply with any of the conditions outlined above, I have attached form MV-700 to apply for a refund, for your convenience.
Sincerely,
Carol Little, Contract Compliance Manager
Nevermind the fact that even before I moved to the UK, I didn't own 2 forms of proof they're asking for, but I certainly don't have it now. So I am humbly admitting that you were right, bookgrl. You can't renew indefinitely without turning up to get your photo taken.
So what this means for me is that I am unlikely to ever drive in the US again, as I don't intend on moving back there (and if I did, I'd have to retake the exams all over again!), and I have zero desire to drive in London, so I don't want to get a UK driver's license. I was just over in September so there's no chance I'll be back over in time to get my photo taken before the expiry period (I only try to go back every 3-4 years if I can help it). I'm kinda bummed, but it's the first major sacrifice I've had to make for severing my US ties, so I suppose it's not too bad.
I *am* going to be annoyed at having to haul my passport around everywhere in order to buy beer though.