So I’ve been playing a bit with watch face created directly using new Watch Face Format.
What can be added to the WFS in the future? Watch:
1. COMPLICATION SLOTS - BoundingRoundBox and BoundingArc
Yes, it’s definitely possible to convert any complication slot to any shape, here in the example, Small Box was converted to BoundingRoundBox and it contains RANGED_VALUE alongside SHORT_TEXT types
From this: <BoundingBox x="0" y="0" width="120" height="120"/>
To this: <BoundingRoundBox x="0" y="0" width="120" height="120" cornerRadius="10f"/>
BoundingArc? Definitely possible - see upper and bottom complications, these were converted from Small Box too
<BoundingArc
centerX="199f" centerY="-61f"
width="450.0f" height="450.0f"
thickness="90f"
isRoundEdge="TRUE"
startAngle="240f" endAngle="120f"
direction="COUNTER_CLOCKWISE"
/>
Notice round boxes of the Small Box complication slots 
2. PHOTO / LARGE IMAGE COMPLICATION - It was assumed that there are not many complication providers for this type of complications. So, small test
<ComplicationSlot slotId="0" displayName="PHOTO_COMP" isCustomizable="TRUE" supportedTypes="LARGE_IMAGE PHOTO_IMAGE " x="0" y="0" width="450" height="450" pivotX="0.5" pivotY="0.5" name="PHOTO_COMP_0" alpha="255">
<Variant mode="AMBIENT" target="alpha" value="0"/>
<DefaultProviderPolicy defaultSystemProvider="EMPTY" defaultSystemProviderType="LARGE_IMAGE"/>
<BoundingOval x="0" y="0" width="450" height="450" />
<Complication type="PHOTO_IMAGE">
<PartImage x="0" y="0" width="450" height="450" pivotX="0.5" pivotY="0.5" name="Image_b9f1" alpha="255">
<Image resource="[COMPLICATION.PHOTO_IMAGE]"/>
</PartImage>
<PartImage x="0" y="0" width="450" height="450" pivotX="0.5" pivotY="0.5" name="Shadow_6480" alpha="255">
<Variant mode="AMBIENT" target="alpha" value="0"/>
<Image resource="wfs_bg_a2a483ab_7510_44f8_8b0e_7a8eb49204d3"/>
</PartImage>
</Complication>
It was necessary to add both complication types to supportedType = LARGE_IMAGE PHOTO_IMAGE
Result? Alongside other 3rd party Photo Image complication providers there is one - BUILT IN! called Media Controller, and it shows now Playing album cover, funny. (Galaxy Watch 4/ Watch6 - Wear OS 4)
3. BOOLEAN CONFIGURATION
Yes, WFF allows developer to add simple switch (toggle) BooleanConfiguration (no more ugly masking, hiding elements or other performance-cost workarounds!)
<BooleanConfiguration id="boolean_test_v1" displayName="ID_SEC_INDICATOR_BOOL" icon="style_wfs_bigjpg_4x_art_none_s2_ed061365_27a9_428b_9116_d691f456fdeb"
screenReaderText="string" defaultValue="TRUE" />
On watch, there are two dots for TRUE / FALSE, so I’m adding screenshots from wearable app customization too
I’ll add more findings later. This just shows what can / should be added to WFS in the future 