As always, I'd say no to the T-7 becoming a medium ship, at least not without some nerfs to its capabilities. Simply putting the current T-7 onto the medium pad with its current statline would invalidate basically every other medium ship as a freighter, rather than the more desirable approach of adding a balanced freighter that would add a bit more choice to the medium freight range.
Nerf the T7? What other medium freighter is there besides the Python? Let's take a look and compare which would be the other choices:
1. T7 - 310 cargo potential, 4 small hardpoints (large pad only)
2. Python - 294 cargo potential. Loses by 16 (just ~5%) but ship hull weighs the same, no small points but gets 2 medium hardpoints, 3 large hardpoints, 2 PP sizes, 1 Thruster size for more speed, 3 Power Distributor and Sensor sizes. And still fits the medium pad.
3. Imperial Clipper - 250 cargo. Large pad, so no choice here.
4. Krait Mk2 - 230 cargo. Loses by 64 to the Python (27%), but weighs 30 less so it handles and jumps better and can fit a SLF, so you can see the 64 trade-off very clearly as the rest is equal to the Python.
5. Orca - 194 cargo. Large pad, so no choice here.
6. Federal Gunship - 170 cargo. This is already way too below the python to be considered a choice, so it's the last one I'm listing here. Ship hull weighs a whopping 230 more than the best choice above and has a smaller fuel tank, so the jump range and fuel range is pretty bad. Clearly designed for combat, not hauling.
If anything, I'd say the T7 would need more capacity, not less, to justify itself balance-wise. An extra size 5 slot for 32 more cargo would still be not even close to what it trades off from the Python in the core module sizes (this is just the weight difference between an A-rated PP 5 for the T7 versus the size 7 one that the Python can use).