If I understand the protocol, the ASP does an on-chain transaction for every round. So I guess 5 seconds is fast enough for a payment to be quick on mobile, but slow enough to allow “plenty” of ASPs to operate. Every bit of time you shave is less blockspace available for ASPs.

Customizable default - its so you don’t have to wait 10 mins for a CJ round & can just close the app relatively quickly once you make a payment.

because every send is a coinjoin, sending is a multi-step interactive process and everyone sending needs to be online at the same time. You don't want mobile users to have to "wait around" for a long time for the round to happen, so you want to to them quickly. Burak picked 5 seconds as an interval....

There are certain things WabiSabi can't/doesn't solve today such as needing additional blame round to collect signatures after non-cooperative participants. I wonder how Ark is solving that. Results will definitely benefit wasabi team while providing an off chain alternative.