I think it'd be great, and profitable for Strava if users could congratulate each other buy buying a month, 3, or even more as a form of Kudos on activities .
Had a friend run their first 5k (or full marathon) reward and encourage them with a gift of Strava premium. The user gets to feel rewarded, the gifter feels like they helped out, and Strava gets some money plus the chance that the giftee will enjoy their time with the subscription so much they will choose to subscribe themselves so Strava gets more money.
Now I don't want to devalue regular Kudos, or make them feel like they're less important. But just give people a way to do something extra for those activities and achievements that go the extra mile.