Some good prices available currently with Oman air between Europe and Asia, lots of availability.
I just booked Jakarta to Milan with a stopover in Muscat for ~#$1300 AUD
Terms and Conditions:
Ticket sales from 07th July 2018 to 14th July 2018.
Valid for outbound travel period from 14th July 2018 to 31st March 2019
Discount is applicable on the Business class base fare ( R ). Taxes & surcharges are additional.
Discount is applicable from and to selected destinations only.
Discount is applicable for Return Journey only.
Minimum stay two days and Maximum stay one month from departure date.
Discount is not applicable to domestic, code share, interline and rail service sectors.
No Stopover Paid by Carrier to be given on these fares.
Only limited seats are available on promotional fares.
Please review fare rules at the time of purchase. All other conditions are applicable as per fare rule.
Edit: If you happen to book a flight that requires a stopover in Muscat get in touch with the airline, there are a few posts on other forums saying that if you ask 10 days in advance this booking will include a free hotel stay.
It's worth noting that Oman Air doesn't have any flights from Australia, and discount is not applicable with code share bookings.
So might be worthwhile only combining with some convenient SEA hubs they service e.g. BKK or KUL.