The usual Tesla usage of Type 2 in EU in other Type 2 regions is shown in the first 3 rows below. Tesla Superchargers basically use DC-Mid for higher than officially rated power output. The Model 3 will ship in Type 2 regions with the Type 2 CCS ("Type 2 DC-High", 4th row), and Tesla seems to have stated that they will add Type 2 CCS cords to Superchargers to match , which implies that the non-CCS upper portion is not wired for DC-Mid usage, or whatever they have done to get away with using DC-Mid at DC-High rates is not possible on the Type 2 CCS (either physically or legally - there's been some discussion about how CCS group doesn't allow adapters and/ or modified ports).
Physically, a Type 2 (AC/DC-Low/DC-Mid) plug (charger side) will fit into a Type 2 CCS receptacle (car side), but the reverse is not true. In theory you could design a Type 2 CCS with retractable DC-High pins and I think I've seen some prototype for that but I've never heard of such a thing going into production - I imagine the added cost and complexity being the reason.
Tesla's Type 2 implementation uses high powered relays commonly called contactors to disconnect the shared AC/DC pins (also true for Tesla's proprietary connector in North America, just different physical layout) from the connector. For each pin that can be either AC or DC, there must be two contactors (one which will be connected to the AC inverter, one that connects to the battery HVDC - and never both connected to the Type 2 connector at the same time which).
Tesla has indicated that the Model 3 will not support (this may be a misunderstanding or legal fiction) using the Type 2 CCS port for Tesla's modified Type 2 DC-Mid implementation, which a naive interpretation implies that simply the pins nominally shared between AC and DC-Mid/Low are permanently wired to the inverter and the upper portion can only operated in AC modes. For safety, the bottom CCS DC-High pins are probably run through contactors anyway as otherwise touching them with the port open would treat you to the direct power of the battery.
Nominally the S/X must have either 4 or 6 contactors (depending on how many pins are used in modified DC-Mid, I'm not sure) - for every shared pin, times 2 (one for each shared pin to disconnect from AC, and to disconnect from DC). Keeping this existing configuration and adding Type 2 CCS would need 2 more contactors for the DC-High pins. However, assuming the 3 really can't use existing Type 2 Supercharger connectors, then it would make sense that they would ditch all the unneeded contactors, which would get them down to possibly just 2 for the charging connector (vs 6 or 8 if it really is physically capable of using DC-Mid still). This was why I commented that assuming it's not a legal problem, it's only a couple more contactors they'd need to equip the car with in order to keep existing S/X connector compatibility plus add CCS.
Here below you'll see pictures of actual plugs, that you would connect to the car. The Type 2 on the upper right is physically the same as what Tesla uses in EU and other Type 2 reasons. The Model 3's receptacle would look like a combination of the "Type 2" (Type 2 CCS) and "Type 2 without optional pins" (Type 2 non-CCS, AC/DC-Low/DC-Mid), seen below that in official renders. The one labeled Tesla is what is used in North America.
Render with the new Type 2 CCS supercharger connector. If a real CCS connector then the DC will go through the two big pins on the bottom, only.
