I'm animating stuff in Flash since 6-7 years. For that whole time I wished someone will come up with some clean and fast alternative not relaying on some plug-in's. I don't mean to bash Flash in here. I still like some things about it. I'm just happy that you guys create something fresh and depending on open, quickly expanding technologies.
I think Sencha Animator is already nice app and has great potential, but still needs a lot of tweaks and additional tools.
I listed some of features that came to my mind during testing Sencha Animator:
Scale tool with an option of proportional scaling.
3D rotation tool. Using current 'type-in-right-value' way of doing things is unpractical in use, unless you want to do some simple 360' logo rotation
Enhanced text controls in UI. Easy way of typing in text.
Adjustments panel for background image. Offset, scaling, transparency, tiling kind, etc. Asking for blending modes for background image is probably too much, but maybe it's possible for you to add it. I know SVG specification supports blending modes, so maybe at least you could add blending modes for SVG based objects. It would open whole new world for creating good looking bitmap textures without Flash. Yeah, I know I can do everything in Photoshop and just use textured images, but then I can't animate things on "low level" (i.e. fluently change color of object without affecting it's texture). Blending modes would also make possible some crazy graphical stuff on web pages. Just think about it.
An option of setting custom density of timeline grid. Having line every 0,5 sec is not enough for precise work with time.
Info panel for images. Just to check how many of them are already used, what is their format, size, resolution.
Custom easing curves editor. If it's complicated to make curve based one, at least make it possible to set intensity of easing and add some more easing profiles. It would be also nice to exchange custom easings between projects, or just to add them to easing profiles list.
Onion skin view with custom (pre)view range.
Info panel for fonts used in project.
General improvement of timeline editor. Currently it's impossible to copy, duplicate and paste frames in clean and intuitive way. Using shortcuts, and 'ghost preview' of i.e. dragged part of animation would greatly improve usability of timeline editor.
I hope you will add some of those features.