So, could we design an Ars Magica game which starts at, for example, around 1875 (the greater Regency era, if you will) and runs until the end of the reign of Victoria? What would it look like?
My suggestion is either that Issac Newton, in his Principia Magica, or Roger Bacon in his New Atlantis takes the role of Bonisagus. He changes how people think of magic. It becomes systematic and non-theistic. How does this differ from Natural Philosophy in the standard game? Well, it doesn;t in a way: what it does it tries to graft the magical machanics into the setting better by suggesting that magical knowledge and scientific knowledge are the same thing.
So, if you have a score in a Form, that acts as an Ability in Lore and Craft rolls as if your Ability score were (Art / 5). So, if you are a Terram magus, you are a great geologist, and if you are an Ignem magus you are great at designing locomotives (which are basically heat transfer engines). The converse is also true: if you are a Gifted person, and you discover a great deal about the creatures of Africa, then you become a better Animal magus. There are a lot of hobbyist magicians, particularly among the clergy.
The negative social effects of the Gift mount with experience. While you are just a bit of a dabbler you are fine: once you become a really skilled magus (20 in anything) people start to shun you.
Mages club together in Learned Societies. Some, like the Royal Society, have tremndous backing, while others are basically gentlemen’s clubs, or even just people meeting every so often in a particular coffee house.
Enemies: well, the French are the obvious candidates. They;ve had a learned society for longer than the English, and they have the whole Napoleon thing going on.
Are there Houses? I doubt it. I mean, someone may say they are a follower of Halley and be really interested in optics, but I don’t see Houses so much as self-taught men who read magic at university, like doctors.