Actually, there are some METZ and SIGMA flashes that do support iTTL but no manufacturer other than Nikon supports off camera CLS to my knowledge other than Nikon.
There is a reason why they are more expensive than other flashes... they are usually excellent quality speedlights that can work with CLS effectively. That said, CLS flashes are nice but has some very distinct disadvantages such as limited range while using CLS and the higher costs of the flashes in general.
Ever since I have learned how to mix and match iTTL and non-iTTL light sources harmoniously, I find that my needs for using as many speedlights has diminished. I'm typically using 1 maybe 2 light sources vs 4-5 before and accomplishing nicer results.