I've been playing the GBC version and noticed a few things from the get-go that could be interesting to implement:
It's constantly in a 2-men cell mode. This has two pros and con: it's easier to manage, minimizes losses, doesn't have units limit (as long as there is recruits at the base, you can keep throwing them at'em), BUT you can't split the team.
Building capacity limit. In the GBC the buildings can't be destroyed really, you can throw a grenade to force everyone inside to come out, but it's two or three men that are in, meaning the building destruction is optional.
Because you can't see the whole map, the pause screen has a "Scan Radar" that shows blips of enemies that are within a wide area (presumably within 256 pixels from the player?). As a feature the scan radar could appear in a corner and not needing to pause to check, also diminishing the need of map checks.
When grenades are "required", there's a crate conveniently placed near the drop point (except in Mission 2 Phase 2 for unknown reasons). Perhaps this idea could be taken into account for a "map patch" that can be optionally applied before starting a campaign (or, alternatively, just have a "start with grenades" option)
I've been playing the GBC version and noticed a few things from the get-go that could be interesting to implement: