There are a couple things we should consider when talking about arming drones such as the MQ-28. First consideration is payload.
I haven’t seen any official figures but similar sized drones often only have a payload of maybe 500kg. That will get you a couple of small missiles or bombs. A fraction of what a manned combat aircraft could carry.
To be an effective combat drone would require you to scale it up and add a bigger perhaps military spec engine.
While this would give you a more capable combat drone that would raise the next issue, cost. One of the appeals of drones is that they are cheap.
The Boeing stablemate of the Ghost Bag is the MQ-25. A far more capable drone with a price tag of around $136 million each. The more capability you want the more you have to pay.
The linked story discusses the USN requirements for CCAs. To summarise, it will be cheap, live a short, hard life and eventually be used for target practice or as a Kamikaze drone.
The planned fate of our own drones might not be much different. During actual war they will be sent on the most dangerous missions often required to sacrifice themselves to achieve that mission. If by some miracle they manage to survive a few missions their ultimate fate might be to swap out its nose cone for a warhead and end its days as cruise missile.
In Australia’s case it has already shown its hand as far as its future capabilities are concerned. Deployable missile batteries, optionally crewed missile barges, SSNs, more naval VLS, long range missiles and eventually hypersonic weapons.
Not hard to work out how valuable ISR and target acquisition becomes in that scenario. Truth is that a cheap disposal drone might be all we need.
“I want something that's going to fly for a couple hundred hours. The last hour it's either a target or a weapon. ... But I'm not going to sustain them for 30 years,” said Rear Adm. Stephen Tedford, the Navy’s program executive for unmanned systems and weapons.
breakingdefense.com