While Ilian can not comment about 11.1 we can make a educated guess since the new release scheme since version 10 makes it more predictable:
dates = WolframLanguageData[WolframLanguageData[], {"DateIntroduced", "VersionIntroduced"}]; (* this is slow, can't think of another way to get these dates/versions *)
tmp = Select[Union[dates], Last[#] >= 10 &][[All, 1]];
DateString[dates[[-1, 1]] + #] & /@ MinMax[BlockMap[DateDifference @@ # &, %, 2, 1]]
Executing gives this range for version 11.1 (but of course also depends on marketing and timing around the year)
{"Wed 9 Nov 2016", "Sat 14 Jan 2017"}
This, however, could be fixed earlier in a 11.0.2 version for example...