I believe JAK/STAT signaling is more connected with the adaptive immunity leg of the immune system, while low-letter interferons are more connected with the innate immunity leg. So different diseases will respond more to one kind of drug or the other. You can recognize interferon-heavy reactions in yourself because they feel cold-like. Frankly, JAK/STAT-heavy reactions feel like creeping death (but only very strong ones--milder ones are just like being tired, and can go un-noticed). Establishment of an autoimmune disease often has an innate-heavy phase during which the disease is presumed to be in principle curable; when it becomes primarily adaptive, it is presumed permanent.
So where does that leave us? Gestational and especially post-partum autoimmune diseases look like good candidates for an anti-interferon. Clearly, some experts think lupus in particular is a decent candidate. There will surely be interest in any disease characterized by cytokine-storms (but the most classic of those is 2-bucket food poisoning, and it's over before you could start treatment). I'd expect that the 2 classes of drugs would be used in combination pretty often.
The potential money from a good RA drug is beyond imagination, so any partnership deal would be exotic and hard to value ahead of time. Lupus is a much smaller market; I'd expect separate licensing for that indication, and relatively sooner. But until the initial phase 2 results are in, this is a pig in a poke. You don't have a drug candidate until you can get effective levels in living people.