Those markets are very slow and hesitant to implement other currencies. There is only one market so far that accepts monero, the other one pulled an exit scam if you believe the various sources out there. So there’s some risk attached.
In an article I read that alphabay, the other market that implemented xmr, sees only 2% of sales in xmr.
But the real reason why it would be very very weird for them to implement sdc (or rather, sdt!), is that Umbra, the marketplace that will be developed upon sdc, might be seen as direct competition. I highly doubt a single market would support that coin, tbh.
So from that perspective, it would be a waste of time, tbh.