Ideally, one could sync (both ways) with their favorite "other" service (my favorites in this case are Hiveminder and Trello), but it seems to me it would be a lot of work to cater to absolutely all user wishes.
What is needed, for example, in case of zapier.com is for someone to make the "zapier app" of WeekPlan: zapier.com/developer/ - it seems easy as long as you already have a RESTful API and a couple of other preconditions.
However, if there are currently no plans for a simple API to WeekPlan, then what I'm effectively asking for is exactly that - an API. Preferrably to the specifications of zapier.com/developer/perfect-api/ or similar.
The beauty is, when there's a simple API to your service, others can help with the other steps. For example, I'm already thinking trying to do one Zapier app for two services that *have* APIs (disclaimer: I'm not a professional developer, so this will be an exercise and a learning curve for me, I'm sure).
Customer support service by UserEcho