How would you want a timeskip to happen?
As the title says, it's something the devs have said they want to do at some point too and I think it's quite possible for the next expansion.
The way I'd like to see it play out that I think is possible and would make sense is for the next expansion to revolve around us activating the new Azem crystal but we're unable to control it perfectly and are sent to a different shard alone. And then either it's a reverse SHB and the Scion's have to come and find us and are aged up because time moves differently between the shards ( possibly with aged up Ryne and Gaia too? ). Or they're simply aged up and time has passed when we return.
Imo it seems like a way of doing it that makes sense, especially since it wouldn't affect the WoL which I think might be a concern that they have. That it'd feel weird if everyone ages except the WoL. But this would be a way of getting around that and still make sense and would also come with some shock factor.
One issue with it would be that it'd be strange we could teleport back to the Source and talk to people when we're not supposed to be able to. Unless they don't want to strand us there, but maybe we just have to do something there and the others can't follow and we're taken by surprise after we're done and return how time has flown.
It'd also add some stakes to shard traveling too, and make it something we can't or shouldn't do carelessly and that the timeskip is the consequences illustrating that.
That's my take at least on how I'd want it to happen.