@aschroeder, Here are the instructions to do the mods and a photo.
Regarding the VDD_TCXO modification, in my opinion the best method is Option 2 that involves using a laser if you have access to one. With Option 1, there isn’t much space between the via and the Murata module to solder a wire to the trace after you drill the via.
tcxo and usb repair v3.pdf (1.4 MB)
Good job for publishing the details, but for me this is a first, using a laser to rework a board.
I have a green laser which is great for pointing out stars in the sky, will that do ?
Hi @LoRaTracker LOL! Off the top of my mind I do not think the star pointer will work well. I had access to an Oxford laser with a 20um spot size. They are used for laser micro machining, micro drilling, etc.
Hey @sslupsky!
Thank you for the detailed information - great job. Unfortunately i think we have to wait for the next version from Arduino. Tinkering with an oxford laser is beyond our possibilities 
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I don’t have the the hardware nor the skills to modify the PCB, so I pursued the TPL5110 route.
There is obviously some overhead, but at least the sleep current is under 50 nA…
Running (I attached a small display for debugging):
Sleeping:
Difficult to tell from the pictures, but are you feeding the Adafruiit TPL5110 thingie with 2 x AA LifePo4 in series as the power supply ?
Pictures are misleading, I was out of battery holder so I add to hack a bit for testing 
I actually use a single 700mA LiFePo4 – one of the 2 batteries in the picture is a ‘dummy cell’ used as placeholder (which can be used when you want to replace 2 ‘dry’ cells by a LiFe)
This is BTW another stupid annoyance of this device: it has an 1/3 voltage divider, so the maximum you can measure is 3v using the 1v reference. So by the time your LiFe reaches 3v, it is almost empty…