That's too bad. I only tried LAS since that's where I'd want the stopover.
However, note that the prices Matrix displays are consistently and substantially higher than once you load it with Delta.
I did not know that.
I'll see what stopovers do to price at checkout.
There's a lot of options here: OGG, LHR, BOM, AMS, HNL, LAS, LAX all interesting cities to have a long layover or stopover in. I got it to build in 14 hour plus layovers at every stop for same price. With hotels and bar tab it would take about 9 days and cost thousands. But a fun experience! (Be better up front of course.)