I love that idea. It always seemed odd that the Highlanders were mercs in the first place when they were, from the start of the Union onwards, an intrinsic part of the British army.
I’d love ‘proper’ ironclads, i.e ocean-going. I want to see a shipment - ‘Victorian Naval Advancements’ that adds a set of additional, expensive upgrades to the dock. Essentially they replace the Caravel and Galleon with Federal State ships, the Sloop and Steamer (ironically the reality is that they would have appeared in the UK first anyway) and add ‘Ironclad Frigates’ tech for Frigates which upgrades them to ‘Arrmoured Frigates’.