Custom icons are more-or-less available in METRO UI (BETA). I suggest using the gallery to select icons for now. I am working on the fix that should allow custom file managers to work as well. Here is an update on some of the requests and where they are on my priority list:
1. Fix issues with custom icons
2. Long press tile to Edit/Delete
3. Updates to Status Bar (new icons: WIFI, Bluetooth, Vibrate/Silent)
4. Custom tile color
Started looking at, found it will require LOTS of work:
1. 2x1 tiles. I am using a GridView and it does not allow column span. So this will require a pretty large rework :(
2. Rearranging tiles. Again the GridView does not seems to be very friendly for drag-n-drop.
Very low on the list:
1. Widgets. My experience is that widgets really slow down the system. Since my goal is a lightweight get-in, get-out launcher, if widgets slow it down too much they will be removed. When/if they are implemented it will most likely be on a separate screen. Accessible from the menu(?)
Anyway, if I missed anything I apologize, I was doing this from memory :)
On a side note, check out this screenshot. Submitted by bamick823 on XDA. The icon pack is available from ubergeekinc on DeviantArt.