So for carrying Ra'ad, a new aircraft is required still.
This can be worked out in two ways:
First: Changing weapon (Ra'ad) dynamics
1. Next version of Ra'ad can be designed to to be carried by JF-17 underbelly. If thats still not possible due to low height of JF-17 then the new version of Ra'ad should be made considering J-31 as platform keeping in mind the size of internal bays.
A smaller design challenge would be a compromise between payload or range. Either a smaller warhead but comparatively larger fuel capacity or a large warhead but smaller fuel capacity. In either case, the range wont match 350 km of current Ra'ad version, probably 150km or 250km, but it will definitely more stealthy.
2. If PAF wants a newer version of Ra'ad with 500-750 km range, means larger size and more weight. In such case a preferable platform would be a twin engine jet. Probably an aircraft that could carry two.
Second: Changing the delivery system (Aircraft)
1. If a new aircraft is acquired would the cost be justified. Mirage 2000 is a cheaper to buy option, agreed, but it brings a few issues with itself too.
a. Old airframes means it will need to be replaced earlier than a new aircraft so its a short term solution. service lifetime is lesser than a new aircraft.
b. Facilities will be upgraded to induct training sims, pilot training, spare part acquisition, upgrade of avionics (at some stage), engine overhaul and other maintenance issues. (This is all cost related)
c. It doesnt have an AESA but does have HMDS/MICA IR/MBDA Apache/and other French related weaponry, apart from being a good (not excellent) substitute for PN naval mirages.
d. The upgraded versions of JF-17 could have benefited more from Rafale induction than Mirage 2000. If this open doors for best French avionics and weapons suite for JF-17 at some stage, then its a great option, however, Chinese are catching up fast in this area too and will provide cheaper(loan etc) and hassle-free( no strings) acquisition of next gen weapons and avionics for JF-17.
2. Considering SU35 or EFT. In longer run, these aircrafts offer much more than Mirage 2000 in every aspect. I wont go in details as they have been discussed many times. I am not sure if induction of Ra'ad would be an issue with these 2 types of a/c.
I will vouch for J-10 also.
3. 5th gen is the future, will PAF always use 4 or 4.5 gen aircraft for delivery of Ra'ad. When J-31 will be inducted, its stealth characteristics make it the best platform to carry Ra'ad (preferable Internally).