So, it's valid to point to the module slot as a cost. But equally this ship has more internal volume than anything we've ever built before, and a boost to Science from its computer core. Given the internal volume, there is almost certainly going to be auxiliary module slot to sacrifice first before Science modules. So we need to ask which offers the the better cost/benefit.
Going up a whole ranking in Tactics is clearly worth an extra cargo bay or a crew lounge given the importance of combat to the design. Like in general rankings are weight higher auxiliary capabilities outside special circumstances, but especially when it's core to our mission profile and creates an amazingly cost-effective combatant.
Okay, but as
@Sayle says in the same post you quoted this from:
Right now, we are not building any Selachii at all, and have no plans to start churning them out again short of another war in the near future. It is not the actual practical limiting factor even in wartime, as we would build mostly Selachii in that scenario.
In short... there is no meaningful cost, other than the module slot.
No, we would not, for the same reason we were not building the Cygnus during the Federation-Kzinti War.