I think if anything it might be good to focus Tixel (sounds like something by Mr Fish) on palette-based spriting to begin with, as this is hard enough to get right. Full 24 bit + alpha makes it into a PS competer, and there's no real way to compete there. The palette-pool could still be 24 bit, but the one you work with shouldn't be imho.
Also, I'm into Annabelle's suggestion about Z & X for zoom.
Been thinking, and there's a couple of features I really miss from Dpaint:

- The way it was full-screen. I'd really prefer one written to be strictly full-screen so you could easily hit the buttons on the right (especially as a Mac user... Don't think it'll happen though, haha. I'd probably do it in something like BlitzMax. Keep it simple, snappy and fast. Windowed mode would still be a one-surface interface. I find customisation makes things more cluttered generally.
- The onscreen palette. This was a nice size and easily selectable with a mouse. One quite radical idea here I have comes from sprite package I once wrote, and I added an extra palette by holding space that was full-screen. The more custom colours you had, the more would appear onscreen, starting with just two colours, then four, eight etc, so the actual hit-boxes for the colours were huge! Releasing the space bar switched right back to the picture. This made palette selecting lightning fast and I'm surprised no-one else did it. I use the same kind of system in my tile editor, just without the hold-releaase so I can tweak tile settings. I digress..
- The grid was spot on. It never got in the way. It was easily turn-off-and-on-able,
- The set of tools. I loved the way clicking on on the top-left did un-filled, and bottom-right did filled. All useful and clear (except maybe the spraycan and 'unjoined' line haha.)
- I also dig how the selected colour and background colour are laid out, really clear to see which is which, unlike PS.
- The stencils. You could lock certain colours from the palette. This was really handy!