This article is a bit inaccurate about XMS. XMS works just fine on the 286; see the original spec [1]. This is done purely in real mode on the 286 with the the A20 line [2] which allows addressing a 64kB area above 1024MB, in combination with the the undocumented LOADALL instruction, which allows addressing even beyond that [3].
[1] http://www.phatcode.net/res/219/files/xms20.txt
[2] https://en.wikipedia.org/wiki/A20_line
[3] https://retrocomputing.stackexchange.com/questions/1006/what...