TLX is a great system, and I like it very much. I don't even have to list the various advantages of the stuff, we all know them already

However, a larger TLX build can be a bit repetitive. You end up either with lots of very similiar corridors, or with a number of rectangular box buildings. A very cool add-on, to loosen the look up a bit, would be TLX-compatible, more or less permanent tiles with more elaborate models. Say, something you can't very well do with TLX - akin to the objectives in Platform Command, or maybe some larger, static objects: reactor chambers (something like the ones in Mel's Derelict), larger machines (like the claw thing , or the sewer outlet from PCON), or even jumbled vents/pipes/ventilation shafts (as in the Windows screensaver).

You could then build these sets on a standard 6x6 tile (or 3x6 or 3x3, depending...), and drop them in the otherwise modular build.

The main idea behind TLX is the modularity and break-down feature, letting all elements fit into flat zip-lock bags. Having larger, traditional structures would kind of negate that advantage

Having scenario-specific terrain features would also mean far less potential customers will be interested in it.