USHPA doesn't have any currency requirements other than you pay them every year. If you got a rating 20 years ago and have paid every year but not flown once in those 20 years, then your rating is still good. But if you fly every single day, but have not been paying for some number of years, then I believe you need to be recertified through some process (which may require an instructor review and/or signoff) to get your ratings back.
I believe the FAA is different. I believe (and it's been a long time, so I welcome any updates) that your license is good for life, but you are not able to fly unless you pass regular physicals, regular (biennial?) flight reviews, and maintain some degree of currency in the category and type of aircraft you want to fly.
I personally think the FAA model is much better and will lead to better safety. But it does end up putting a burden on pilots. So the question is what degree of currency do we think is appropriate? Here are some options I pulled out of the air:
Option 1. No requirements at all. Ratings are good for life, and that's it.
Option 2. One flight per year for currency. If it's been longer than that, then you need to be checked out by someone (instructor or not?) who is current. This could be as simple as your buddy asking you a few questions or doing whatever they feel is appropriate for them to sign you off.
Option 3. Same as Option 2, but if it's been longer than 5 years since you've flown then you need a current instructor to sign you off. The requirements for the sign off are up to the instructor since he (or she) will be taking on roughly the same responsibility for your flying as an original instructor.
These options aren't intended to form any kind of coherent plan, but they are intended to get us thinking about what we think is tolerable and appropriate.
Thanks for any comments.