A re-engine job to something less thirsty would definitely be in order.
I'd also say that four petaled tail pipe/speed brake arrangement would have to go. I imagine a lot of weight in hydraulics to move all that heavy, heat resistant metal must have been crammed in. Let the tail pipe just be a tail pipe and redesign lighter weight material speed brakes further forward of it in perhaps a similar arrangement to what the Sukhoi "Fitter" family had.
Also, would wider chord tail surfaces benefit the Thud? The fin and horizontal stabilizers always looked a bit undersize to me in relation to the rest of the aircraft.
On that matter, could the wing be reworked with higher lift devices that could reduce take off and landing roll and give improved low speed handling? Full span flaps on leading and trailing edges perhaps.
How about a later, lightened version after countermeasures reached a quality that some armor could be dispensed with and composite materials worked in?
As for foreign users....
The Thud in imperial Iran probably wouldn't have been out of the question as a forerunner and supplemental aircraft to Phantoms.
Any country that had the Canberra for strike purposes and needed to replace it; Argentina, Australia, India or New Zealand for example could have been good Thud candidates.
The maritime strike angle has been mentioned already; this could open the door to countries like Germany, Denmark, Norway and Japan.