Honestly, I do believe that fighter bays will use an internal slot. That being said, I also wager they will be quite powerful.
To put into context, I was chasing an Anaconda the other day with two Sidewinder escorts, both armed with the same two small weapons like the fighters are. And those two Sidewinders continuously attacking me really messed with my shields and I had to flee. So I'm curious to see how well those fighters will fare once they are implemented.
The Keelback, just like the Federal Gunship, suffers in that they are not strong enough for the base cost. So I suspect it's due to balance for the fighters when they come out this summer. FDevs have the math in place, so they just need to ensure the fighters fit that math in testing.