Even if you can't figure out the 2-way wormhole, this still has a lot of potential. The plotbunny about Methos's son seems more exciting, but this is the one that's the most complete. You could have Methos coming across the SG1 on different worlds while he's on vacation, and both parties are wondering why they keep crossing paths so often. SG1 keeps asking Methos questions about his home world, thinking that a planet of beings that don't die could be useful allies, while Methos tells half-truths that give a completely wrong impression to SG1. I like the idea of them giving him a tour of Earth. At the end, either they see someone on Earth recognize him or one of the members of the SGC dies and comes back so they finally figure it out. Of course, that leaves open how the SGC deals with Immortals.