I found this interesting A SparkFun Feather Board? - Hackster.io
Is this “the standard” for today’s maker boards? Even meadow used this form factor.
What is next? A a FEZ in this form factor?
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It wouldn’t be hard, just reformat a G80 TH into one of those. All it needs is a new board layout and a battery charging circuit. If you could pair a G80 with a ESP32 that would be ideal. I suppose Integrity Micro’s Electron design could be easily formatted into that.
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and one this just to add an expansion board to turn into arduino compatibility mode
(with and plug’n’play board with headers)
I was going to comment that the battery charging circuit on a number of these boards charges the battery at the same time as drawing power from it and that is not good as the battery charging never switches off but Sparkfun have included a MOSFET to switch off the battery during charging. The battery charge IC also switches off after the charging is complete.
I ran into an issue with one board based around this type of design where there was no MOSFET and after a few months of use, the battery was starting to expand. 
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Only by checking the schematic for it or reverse engineering the PCB.
This works well.
https://cdn.sparkfun.com/datasheets/Components/General%20IC/33244_SPCN.pdf
https://www.sparkfun.com/products/10217
Those are standalone chargers and not designed to power the circuit at the same time. You could use them but you would have to include some form of circuit to switch out the battery when the external power is applied.
This is what Sparkfun has done with the board above.
Is charging circuit and LiPo part of the expected “feather” layout? We have been staying away from charging circuits for liability reasons. Any recommendations on what seem to work well?
Years a go, I looked and I couldn’t find a single chip that does both, charging and powering a circuit!! You would think this is needed and a single chip would charge the lipo and automatically switch to charge and power the circuit. Maybe that magical chip exists today. I need to look into it again.
Ti do lots of lipo white man’s magic which they call power path.
I have used BQ24232 in the past which work really well. They have been out since 2008 so your Google Fu must have been weak that day or your search was really long ago 
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Most of those lipo cells have internal circuitry nowadays that prevents overcharging and greatly reduces the risk and liability. If the cell explodes it the cell manufacturer that did something wrong. Just don’t offer the cell for sale on your website 
Lol I have never heard this before. I will surely use it.
May of the 18650 cells on the market have no protection at all. They are designed for use by manufacturers to include this in their own boards. I’ve been looking at how to do this with 3 cells in parallel, each with their own protection circuit. So far I have not found an IC for this. Most of what I can find are for serial connection cells.
I am working on a design to power a heavy load Android powered board with enough power to send an SMS prior to shutdown. Took me a while to find the LTC4162-L that can provide the higher current. Most of the TI parts are designed for lower power devices.
This seems to be something the US is pretty good at, lawsuits that is 
I know a lot of small companies who are reluctant to distribute to the USA for this very reason. I even worked for a UK company years ago when a US client tried to sue us for using their logo on our website. It was a simple mistake by our web designer, which we promptly removed. I ended up losing my job because the court case costs took down the company. 
The US company lost the lawsuit too, by the way. 
Wow, that country it too litigious.
What do you mean by “power the circuit at the same time”? also where in the sparkfun board do you see a circuit to switch out the battery?
The mosfet disconnects the lipo from the ldo when plugged into USB.
Without the mosfet the battery is constantly draining and charging which is not a good thing.
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If you can download the schematic or Eagle files, Q1 is switched on when the USB is disconnected supplying power to the circuit. When USB power is present, Q1 is off and the battery is disconnected from the circuit and now charges via U1. Not that when charging, with Q1 off, the battery does not supply any power to the U3 regulator. D2 ensures that the battery does not supply power to U1 when the battery is in the circuit.
Ok, I see, I though you meant on the second board that I posted.
What happens when you unplug the USB, is the supply uninterrupted or does the board reset while switching to battery?