I've tinkered around with making an adhoc homebrew fantasy conversion of Battletech in the past, but now I've decided to go ahead and make it into a full-fledged game with rules and setting.
The setting basically takes all five of the Great Houses we know and recasts them as fantasy human empires. Each empire is also attuned to certain elemental magics: Wind/Water (in the form of ice) for the House Steiner/Lyran Commonwealth stand-in, fire/life for the House Kurita/Draconis Combine stand-in, life/earth for the House Davion/Federated Suns stand-in, earth/death for the House Liao/Capellan Confederation stand-in and wind/fire for the House Marik/Free Worlds League stand-in. Not that any elemental magics are forbidden outright to anybody, just that each faction favors a certain style.
The lesser Inner Sphere powers: Comstar, the Free Rasalhague Republic and St. Ives Compact and the Major Periphery States also will have their counterparts. Comstar gets represented by a reclusive religious order which serves as arbiters between the empires and controls the fantasy equivalent to the HPG network. The Taurian Concordat will be a Dwarven nation and the Magistracy of Canopus will be a Wood Elf nation. Pirates will be cast as Orcs and Goblins.
As for the Battlemechs, they will be magical engines of war - the ultimate expression of magical might and artificers craft. Attuned to the few mortals that can control them, they are crafted in the shape of giants (biped) or beasts (quads). Battletech lasers become force bolts, ACs become fireball launchers and PPCs become lightling bolt throwers and so on. Instead of measuring heat as a limitator, the fantasy version tracks reality - the more magic you perform, the more you affect local reality - instead of ammo explosions, you get reality snapping back, instead of shut downs, you get spell locked and so forth. Jump Jets become teleportation, stealth - invisibility and so forth. Beasts will generally be designed around vehicles for large ones, Battle Armor for small ones. Infantry stays about the same. Aerospace Fighters will be Dragons.
Any interest?