I skipped revision 3 because I ordered the board and very shortly after that I ordered revision 4.
In revision 4 I made following changes 

• reduce PCB dimensions further
• smaller holes for the necklace clips
• put solar panel on opposite side of the SMD components
• put all SMD components one one side of the board for easier assembly
• smaller PCB hole for the supercapacitor
• select a new LED that can be reverse mounted on the PCB 

I selected the KPTL-3216SURCK-01 LED from Kingbright. According to the datasheet it has 550 mcd at 20mA, so more than the Wurth 150060RS75000 which has 250 mcd. 

What I've learned from this redesign

• LED viewing angle is actually very important for visibility. I found the new Kingbright KPTL-3216SURCK-01 LED brightness disappointing. It has 70 degrees viewing angle while the Wurth 150060RS75000 has 140 degrees. That is perceived much brighter from different angles. 
• The reverse LED hole in the PCB actually limit the viewing angle and the visibility
• the necklace actually interferes with the USB connector
• the smaller PCB hole for the supercapacitor is good for the epoxy resin, it is now well glued to the board
• I dont like so much the through holes for the supercapacitor because the leads penetrated to other side of the PCB and touch the solar panel