MR (Mid Range)
It's all about marketing. Nobody wants a short range. That is why there isn't a short range Model 3 option. LOL
I think it is worth keeping in mind that the term “Short Range” or “SR” is not a Model 3-related term that Tesla uses as far as I know. It’s something that started being bandied about on TMC and elsewhere online.
When the 3 first went into production, Tesla announced that the car would initially only be available with the “Long Range” battery option, and that the “base” version would be available later. Then several months ago there was the surprise announcement of the “Mid Range” version at a lower cost. The $35K base Model 3 is coming later this year. Tesla is not calling it the “Short Range” version, for good reason, which you point out.
Back to the S/X 75D discontinuation announcement: I agree with many posters in this thread that it seems unlikely Tesla will only offer a single S/X battery size, whether it is 100 or something greater that results from the switch to 2170 cells. If Tesla did that, the base price of the S/X would rise significantly and sales would suffer.
As noted upthread, Elon tweeted yesterday confirmation that S/X pack sizes going forward would no longer be designated with numbers. That does not surprise me; it’s the right thing to do for many reasons. I expect that, like the 3, there will be a base S/X battery and a “Long Range” battery option, likely starting next Monday.
SPECULATION
It seems reasonable to assume that this change in battery designation will be done at the same time as a significant change to the battery packs themselves. We know the 75 pack is going away on Monday. We know that Tesla iterates and improves as rapidly as the technology allows it to. The 18650 is now an “old” cell type. The 2170 is Tesla’s “new” cell type.
If production capacity is available, it seems inevitable that Tesla will switch to the 2170 for S/X packs, which will result in greater total pack capacity in the same volume (the entire pack architecture would need to be redesigned to accomate the slightly larger cells but since there is no more room in the vehicle for a bigger pack enclosure without a massive chassis redesign, I suspect Tesla has been able to accomplish that).
So my expectation is that on Monday, Tesla will announce new EPA numbers for the base S/X, from 259/237 to something like 300/272. That will put the base S/X well above the base Model 3 at 220 and better serve to differentiate the two model lines.
At the same time, Tesla will announce the EPA numbers for the optional “Long Range” S/X battery pack as something around 385/340, raising the bar for the competition and maintaining Tesla’s huge advantage over the various “Tesla killer” full size sedans and SUVs that other manufacturers have announced.
/SPECULATION