There are a number of different factors you'll need to consider when designing the standards. The first is "what is the design goal of the modules." That's a more complex question than it appears.
The obvious answer is "compatibility", but that leads to the question "compatibility with what?" Just TheGauge modules, or do you want to be compatible with others as well? If so, which others?
The second part of the design goals centers around "what type of model railroading do we want to focus on?" Generic MRR? Operations centered? Scenery? Public display? Design for DCC, or not? The standards that would derive from each of these will be different, to varying degrees.
The third part of the design goals centers around complexity. How complex or simple do we aim for in the construction, transport, and setup of the modules? An aspect of complexity is the availability of materials to the builder.
With the forgoing on the table, the single most critical element in modular standards is the interface between modules. The interface consists of track setbacks, track spacing, electrical connections, and the physical interface between the module benchwork. The last is perhaps the simplest: the interface must be smooth, perpendicular to the plane of the track, and provide sufficient area for clamping to other modules.
Track setbacks are trickier, but most of the challenge in setbacks is merely visual. In truth, it doesn't matter whether your track is set back 1" from the front edge, or 10", as long as viewers don't mind a "pier" like look to the modules, some sticking out further than others. The setback from the ends is a little more critical, but given the remarkable facility that module builders have of getting "close" to the standards, but not actually at the standards, one could almost accept that X is the target, and have flextrack and Xuron cutters at hand.
Track spacing, however, is an issue with little room for variance. Unless the standard is going to be a single track, then the design goals must drive this factor. Off hand, I don't know what the spacing between tracks is for N Track, BendTrack, or TTrack, but unless one has compelling reasons to vary from those, I would suggest either N Track's or TTrack spacing. Doing so will allow you to mate up with those standards, albeit without full functionality, and probably not within the context of a 'sanctioned' set-up where everything must meet NTrak or TTrack standards. BendTrack is a little tougher, because it effectively has 2 pairs of tracks at each interface, but if one is willing to consider treating each pair as a distinct interface, it is doable.
Finally, there is the electrical interface. Here, I'll simply come out and state that the standard should be DCC friendly from the gitgo. That means use 12g wire. Second, each distinct line on the module should have its own bus. Third, each bus should terminate in blocks on each end. From the terminal blocks, connection lines with appropriate connectors can be run. The advantage to this method is it is very easy to change from using Molex to Cinch Jones to Powerpoles to whatever connectors between each module. It also allows you to run feeders out from the terminal blocks to the track, rather than tapping directly into the bus wires.
After these standards are sorted out, then other elements can be addressed. Height from floor, length increments, minimum and maximum widths, backdrops, minimum radius, maximum grade, turnouts, track code, etc. I would suggest that the minimum radius be no less than 12", but also no more than 15". I also suggest that the maximum grade be established at 2.5-3%. One of the most bothersome limitations for many people with the existing modular standards is their two-dimensionality, and BIG curves. Yes, we all like to run on big curves, but the radius in NTrak is so great that there isn't much room on a 4' module for variability in the track plan. This and the 3 lines, no grade, and "fixed" entry/exit points for the track are the reasons that N Trak modules look so much alike.
Remember, at the most fundamental level, there's only two things that must be standardized: how the tracks meet up with one another, and how the electrons flow from one module to the next.
