My takeaway from the feedback was 1. doing a Battletech clone is problematic, but 2. some of the mechanics I envisioned are worth pursuing. Honestly, I had qualms about the first problem right away. It seemed difficult to do a mech-type battle game without copying Battletech. Further, though I was into BT for a time way back in middle school, I have hardly played it in the last 20 years. So while working on even these very early brainstorms I was trying to think of a different genre that would work equally well, but nothing seemed to fit.
Last night it occurred to me that the mech battle mechanics would nicely fit the bill for just such a system. Rather than a full-fledged RPG, I envision a board- and tile-based dungeon crawl. The battlemech's tracking mat and tiles become the fantasy character's sheet. Each part of the body can absorb a certain number of hits just as before. Heat build up becomes fatigue, and heat sinks equate to stamina or fitness. Heavier weapons use more cards, causing more fatigue. More powerful weapons get more dice (more chances to cause more hits). Just about everything transfers over.
One change is in the nature of movement. Clearly a one-on-one, mapless dungeon crawl would be very limited, so instead of the simple distance heuristic, characters and monsters have a map to move on. The walls would be predrawn, but each section of a room would be randomly placed as 2x2" tiles. The tiles have a 3x3 grid of movement squares, and each square can contain treasure, a monster, or nothing. As the characters move through the dungeon, and depending on the strength of their light source, the tiles are flipped over.
The game would support several players with their own characters and one player as the "monster master". They'd control the monsters and adjudicate any rule questions, but unlike a traditional DM, their role requires no preparation or improvisation.
Those are the basics of the game mechanics. As for backstory, I'm thinking something like this: you've been tracking a diabolical sorcerer for weeks. You have identified his lair and uncovered his plot to open a rift between dimensions, flooding the world with devils and demons. His magical power will reach its peak with the lunar eclipse. You now stand at the entrance to the cavern, knowing that you only have hours before the eclipse, and the fate of the world depends on you... Cheesy? Yes, but it'll do for now.
Aside from this standard random dungeon romp, I could see people setting up specific dungeons, perhaps even adding in continued storylines and roleplaying. At its base though, the game would be a board game meant to provide a little quick relief for people hankering for a more involved D&D type adventure.
That at least is my vision for today. We'll see where inspiration leads me tomorrow.