Yeah, there aren't a lot of options. Here are the tripartite eligible nations which competed at the worlds, continental or final qualifier.
M1x - *
W1x - * * *
Nations with a * means they already qualified in a different event so chances of winning a tripartite quota is lower. If we exclude nations which have already have a quota in the W1x then we are only left with Malawi and Sudan so I think there's a good chance that either, one of the * nations get chosen, a nation which did not take part in any qualifier gets chosen (like Niger in 2012) or like in 2016, the quota gets reallocated.