The idea of mixing the medieval ages and the present is pretty incompatible. Why bother stabbing shit with a sword when you can shoot it from a half mile away? Why put a guy on horse-back to deliver a message when it's quicker to call the person up on the telephone?
You also have to stop to consider that from a societal perspective it's harder to justify feudalism in the modern world. Between the then and now you have nearly a millennium (depending on the beginning reference year and now) of time. You as well have to consider that for that period there was little or no common national identity. If you were born in a village, you would stay in that village and it's rare you'd even leave the county let alone have a clear idea of the wider world beyond the farm. You would only be significantly aware of and attached to the township the same way as you would be for a nation now; only significant events might force you from home (forced conscription for example).
The big part of the modern world is the formation of and holding of a national identity. You don't identify by your township or village or city anymore but you identify with the broader nation. And with that development of a national identity questions arise over the well-being of common citizens or a broadening of prospects for ambitious people either military or intellectual. Nationalism opens the door to such things like National Liberalism which either means people become so aware of the concentrated control of property in the small class of people on top they either revolt to break down the land holdings of the feudal crown of society to make the King's Lands public lands. From here government becomes a constitutional monarchy or a parliamentary republic.
This change can also be facilitated by the development of technologies that make it easier and cheaper to travel or communicate across the realm and over a generation of using and deploying this people will quickly realize their world is broader than it was during their father and grandfather's times and will likely facilitate the rise of a sense of National Liberalism.
Really, the incompatibilities of melding a medieval world with knights and swords with a modern society leads to so much internal universal conflict it would explode on itself before the plot happens. Even those institutions we might call "feudal" in the modern world have long shed their medieval aspects to be modern authoritarian dictatorships/absolute monarchies. There's no feudalism left in those, just bureaucratic nepotism. Or you would at the least be pushing a universe like 17th century Europe; but that's still the transitional period from old-world dynastic states to the modern nation-state and doesn't really reconcile the two.
Steampunk works because it uses technology not far detached from the 19th century and uses the trappings of the 19th century. It's not really a mix past-future because a lot of the cliches and tropes in the genres are dependent on a century-long period where the general technology used was developed and deployed (steam power, gatling guns, airships, trains). It's not much of a stretch for artists and writers to re-purpose Victorian-era technology and aesthetic to build a fantasy world where steam-power plays a much more central role in a society that looks or functions as a modern of futuristic world.