They do have jets, well technically speaking turbine engined aircraft. The GIV and the Learjet are 'jets' as such. Naturally you mean jet fighters or attack aircraft and no they will never get those.
To summarise my thinking and a few others.
They're expensive to buy, operate and maintain.
You'd also need a dedicated military radar system to control them. That would be nearly as expensive.
You would need to improve the facilities at Baldonnel and maybe even lengthen the runways.
Pilot training would have to be changed radically as would maintenance training. Manpower in the Air Corps would need to be increased to cope.
You would have to accept the fact that they would crash regularly and pilots would be killed. That's the nature of fast jets. They are dangerous. So attrition replacements would be needed.
You'd need missiles and bombs, also very expensive.
But mainly, we don't need them.
WE don't need the PC9s eithere but thats another argument.