It would be really good if this board could provide some mounting holes in order to secure it in our projects. Right now we would have to solder the board onto another protoboard with mounting holes in order to secure it in place.

Many DIY builders use Open Source CAD programs (KiCAD for one) instead of licensed programs like Eagle. It would be very nice if there where a KiCAD module and library of Sparkfun ESP32 Thing for us to use! There is a Eagle script plugin that may help converting your existing Eagle schematics to a KiCAD module/library: https://github.com/lachlanA/eagle-to-kicad
Could you please give it a try, since I don't have a Eagle license to try it myself.
Thanks!

If any of the issues mentioned are known and intentional, please omit.

(1) Need PROD_ID for ESP chip in design

(2) Name for ESP in design currently has a "$" symbol in it

(3) 20K res not present in SPARKLE BOM

(4) 3.3V trace and via at the top of the ESP are a bit off. The top trace does not fully enter the via. I think it could be fixed with some very minor rerouting of that trace.

(5) I think we should add 4 rectangles of tRESTRICT to prevent the GND pour from generating the little tabs on each side of the ESP center GND pad.

The P-channel MOSFET for switching VIN from USB or battery seems to have its drain and source swapped. This makes the circuit always use the battery voltage, when USB drops below that 4.2V. Since this isn't usually the case, that mostly isn't a problem, but it may occur in some cases, that USB provides such a low voltage that the ESP is powered half from the battery, which may trick the charger into thinking the battery is not fully charged, which may result in overcharging. I am no expert, but I think this is a problem that needs to be fixed.
I was trying to use the voltage switch from the Thing's schematic, implemented it already in my layout and then it came out to be wrong.. without D2, Q1 will always be either saturated or the current will flow through the body diode. Unless that's expected to work this way.

Edit: it's implemented the same way in RP2040 Thing, ESP32-S2, ESP8266 and probably other Things. Please, correct me if I'm wrong (which would be absolutely expected).