I think you're a bit to focused on the "flexibility" of adhesives tbh. It's not the flexibility of an adhesive that makes it suitable or unsuitable for floor tiling per se, providing the substrate is stable and sound - it's the power of adhesion it provides, particularly during and after stressing circumstances, such as heating, water immersion, freezing, etc. Dispersion adhesives tend to be a bit more sensitive to such circumstances than cementious adhesives.
Some dispersion adhesives
are suitable for floor tiling according to their manufacturers,
BUT dispersion adhesives aren't suitable for use with very dense tiles (especially not large ones), such as various grades of porcelain, and natural stone, which are the normal choices for floor tiles, mostly because of how dispersion adhesives harden, and that kind of makes the whole discussion moot.
More on the subject of adhesive flexibility:
Choosing adhesive and grout with standards as a general guide http://www.tilersforums.co.uk/tile-a...tml#post146623 
bal blue star-flexible-surely not!? 
Linear Mode
