Depends?
The 8 models were SIM-free from day one. No reason the XI can't be SIM-free on launch. Especially in light of the X was not as big a seller as hoped, do not see why XI would be a huge hit (ala when the 6 came out: truly different [big screen] phone from Apple]).
Extrapolating out, the Plus models sell less than the "standard/small" size, so, the XI+ might not be a huge draw, so, no need to vendor lock the initial sales (ie. might not be a rush for people to upgrade, so, might be an incentive to offer SIM-free day one).