It seems that everyone has been shocked by this development, but the available interpretations are missing few points.
I read this development in 3 ways.
1. Technical
Thank you guys for increasing my understand regarding this issue. We all recognise that this is not an easy step, and required considerable amount of expertise and conceptual thinking to create this match-up.
Pakistan has lots of other important programs, so PAF is not in a position to divert it’s technical or financial resources to this program, unless the intention was to derive broad benefits from this achievement.
Firstly, I suggest PAF wanted to prove to themselves what they can do, and second prove it's internal technical capabilities to the rest of the world.
2. Immediate
By developing a BVR capability on the Mirages, it adds another complexity, therefore costs of operation on the IAF towards any intended confrontation with Pakistan, possibly deter any intentions that may have been brewing. It immediately increases the potentially available BVR capable platforms for PAF. And, in the presence of Block 3, J10’s and AWACS the new capability of Mirages is very much deployable as part of a package.
3. Long term
As far as I am aware PAF does not maintain a credible reserve force, something many major forces tend to establish with time. Any of our older fighter aircraft’s are not fit as a reserve force for modern warfare. But, by developing such a capability in the Mirage, it allows the PAF to create credible reserve force even after their retirement, and with the support of other platforms, the Mirages should be able to provide a decent option for capability enhancement in a short war into the 2030’s.
PAF would not make this effort and divert resources, for something that will be out of service in a few years, it already has its hands full. This effort provides the PAF with immediate capability boost, plus a long term platform on which to fulfil the numbers game. They will only need to be active for a short war, if it came about, that’s enough to provide extra cover as part of a wider package.
I think in those 3 scenarios, this development makes a lot of sense. Plus, the enemy will always be thinking how many aircraft have been converted, which will create a constant lack of certainty in their planning.