I really like my 600EX-RT flashes, but there are a couple of things that would make me dump all of them immediately:
- first, my new RF 800 f/11 lens is a really dim lens that could need a flash to accompany it with a little more power. Especially, at more than 500 m the 600EX tends to become a little too dim. So, more power would be appreciated to illuminate the scene to help this lens.
- With animals, but also street photography or even portraits, a purely IR flash would help in the field, not to shy subjects away. White balance might be a bit tricky, but I'm sure is doable, come on, Canon.
- third, I find the 4xAA batteries a little flimsy to change. I would much prefer the new flash to use only one AAA battery, and a reversed-polarity compensation, so I can just throw that battery in whichever way I prefer. I would even prefer it to use CR2032 cells, but I admit they are too expensive.
- Then, the flash needs to be much much smaller in the bag (but not too small, or I might lose it) and lighter on the camera. Also, this would make it much cheaper as less material is needed.
- I also would like advanced-advanced AI features, eg the flash should refuse to fire if the scene isn't worth it.
Pretty much any of those features would make me swap my flashes in a flash, other than that, I guess I would stick with my 600EX-RTs.