Thanks everyone for keeping us updated with new information. I have updated the main post.
There's still some speculation that Apple will release a sim-free iP6s in the coming months, but after looking at the specs of the current phone, it seems that the iP6s already has every relevant band supported. Take for example:
iPhone 6 sim-free - Model A1586/24:
CDMA EV-DO Rev. A and Rev. B (800, 1700/2100, 1900, 2100 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
TD-SCDMA 1900 (F), 2000 (A)
GSM/EDGE (850, 900, 1800, 1900 MHz)
FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)
iPhone 6s - Model A1633/34
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30)
TD-LTE (Bands 38, 39, 40, 41)
TD-SCDMA 1900 (F), 2000 (A)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
The new iP6s supports more bands than last year's sim-free iP6. The only difference being the sim-free's support for Rev. B CDMA. With the new iP6s already qualifying as a world phone, and if all the paid-in-full phones are sold unlocked, I am inclined to think that Apple will not release a sim-free version of the iP6s, as there is no reason or benefit to do so.
What more benefit would there be in Apple releasing a "sim-free" version? What would be different?