Welcome folks; I don’t think queue slots should scale 1:1 with additional buildings per-line.
However, as someone with 8 EXT, 13 FRMs and 11 INC in each of their own respective lines, one of the biggest issues is actually scrolling to the bottom to find out what status my queue is in!
Having a single line is useful if you’re targeting a specific ratio with different duration batches/recipes, but for high-variety buildings (BMP) the additional slots from HQ upgrades aren’t sufficient
A solution here would be an option to split production lines once you have a threshold number of the same building (6, maybe 8) to balance the benefit of more queue slots with investment; alternatively have it linked to experts somehow, with the 5 default slots and additional slot for experts 2,4 and 5.
While these would be nice, ultimately it is currently in a good state, with some, but not an overbearing incentive to get PRO for recurring orders