I expect if there is an XML3 that it will be similar to the XPL2 in die size and output.
The SST90 is interesting; we don’t see many incorporated in mods. It should be able to pull around 15A from a good single cell and provide ~3500 lumens I estimate, based on data from the datasheet.
If you are interested in high output 3V emitters, keep your eye on the Nichia E21A and E17A. They are 3V LEDs with small packages that can be grouped together to make XHP70-like configurations. There are currently heat dissipation issues because of the non-standard footprint of the emitters, however. Nichia E17A/E21A series (April 19th: updated with output tests in the OP)