Several of the subsytems I've added or considered have to do in some way with representing combat. This is because combat is such a major part of how D&D expresses its rules, so more knobs in that area makes it easier for me to emulate the feel of D&D, even if I'm opting for a different mechanical expression.
To that end, I'm interested in something that can be used to show spatial relationships for the purposes of range and combat interest, and which create an opportunity for players to use a miniature as a marker if they choose. Currently I have a pretty simple Zone system written up, which allows for terrain effects, multiple melee engagements, varying weapon ranges, and a sense of positioning. Some version of this will be around regardless - arguably Blades already has it, informally if not explicitly, in that these sorts of things can be true in the fiction even if they're not directly called out by the mechanics. Defining them gives a hook for other rules to hold onto, though.
On the more extreme end I'm considering what I've been referring to as a "ladder" system. Basically, I like the idea of there being some kind of more granular tactical movement, but I'm not a fan of being forced into battle maps or miniatures use - the latter can be fun to have but the former are always a ton of work to structure correctly and make look decent. As a result, I started looking for a system that abstracted out absolute position to more of a measure of positional advantage. The best framework for that I've encountered is dogfighting rules for airplane-focused games, and the first one that came to mind for me was Tachyon Squadron.
Basically, each zone would be represented by a series of bands, and individual engagements in a zone by lanes within that zone. Actions are resolved from top to bottom, with the set of actions allowing for different sorts of incidental or focused attacks based on relative position on the bands, and different types of movement. This sort of system would add a lot more interest into combat encounters, and consequently give me more options for designing combat effects, and does so without needing anything more than a reusable printable worksheet or graphic. The cost is that it puts more of a wall between resolution of combat and noncombat encounters, which may screw with the game's flow and risks being overkill.
I have yet to write a formal adaptation of Tachyon Squadron's rules for this use case, but it's something I'd like to test out. Even if I don't end up using it, "abstracted positional advantage combat system" is sure to keep rattling around my skull the way Origins, Abstract Weapons, and Die Ratings have.
