Considering the lift of migrating an entire platform of maybe millions of live production, business-critical sites while making sure that nothing breaks, current functionality is at least maintained (if not improved), is easier said than done. That’s not to say that the possiblity is not considered, it’s just not considered a big-enough priority right now.
All this to say, this is not planned on any short-term road-map. Maybe one day this might happen, but as I mentioned, it’s best not to hold your breath. If it’s very important for you to have DNSSEC, you can definitely check out other platform that might match your needs closely.