Depending on exactly how skill challenges work when you're actively competing against NPCs (like the "running from the town guard" example vs. "researching an ancient temple"), the increased-difficulty-leads-to-bonus might also represent your taking an action that makes your task tougher but also makes it harder for your opponent to follow you. The new World of Darkness system uses this sort of mechanic in its foot chase rules, where you can take a penalty on your roll to force the other person to take a like penalty on theirs, representing things like breaking stride to kick over a garbage can or slam a door behind you.
To use the wall example, maybe there's a market stall against the wall that provides handholds (Easy check). If you're feeling cocky, maybe as you clamber up the stall you deliver a few good kicks and partially collapse it. This ups the DC to Difficult (both because you're destroying your own handholds and because you're "losing time" breaking stuff instead of getting the Hells out of Hommlett).
Granted, that explanation makes more sense if a skill challenge involves opposed rolls, but if it is an abstracted system where only the PCs roll, then a bonus to your next check is functionally equivalent. Either way, I'm very interested to see the full text of this system, because it sounds like what we're hearing from D&DXP is only the tip of the iceberg.
To use the wall example, maybe there's a market stall against the wall that provides handholds (Easy check). If you're feeling cocky, maybe as you clamber up the stall you deliver a few good kicks and partially collapse it. This ups the DC to Difficult (both because you're destroying your own handholds and because you're "losing time" breaking stuff instead of getting the Hells out of Hommlett).
Granted, that explanation makes more sense if a skill challenge involves opposed rolls, but if it is an abstracted system where only the PCs roll, then a bonus to your next check is functionally equivalent. Either way, I'm very interested to see the full text of this system, because it sounds like what we're hearing from D&DXP is only the tip of the iceberg.