My guess is not fantastic. Here's an older version of the board the article mentioned, along with some benchmarks comparing it an RPI:

https://www.phoronix.com/review/visionfive2-riscv-benchmarks...

It performs pretty poorly compared to even equivalently cheap hardware (~100 USD).

Performance depends on microarchiteture, not on price. It performs well compared to Arm boards with similar microarchitecture i.e. Pi 3.

Price is related to production volume. Raspberry Pi boards sell in large numbers and can thus be priced more keenly while retaining a profit margin.

We already have a bunch of SBCs with the same core, it's similar to the Raspberry Pi 3, probably a bit faster, but slower than the Pi 4.

See "VisionFive 2" review: https://youtu.be/ykKnc86UtXg

This is more up to date even though the board is much older.

At least as important to me, is what is battery life like? With a 61 Wh battery on what is essentially a mobile processor, can I get 20+ hours of use out of it?

A VisionFive 2 with the same chip uses 3.4 W idle, just with automatic down clocking (I think 375 MHz is the lowest). So that would be potentially 18 hours from a 61 Wh battery. But a laptop also has to drive a screen backlight. On the other hand, maybe the JH7110 has has some lower power sleep mode that was not being used by the software on the VisionFive 2.

Using the JH7110 chip they are starting with, somewhere around the last Pentium 3s and PowerPC G4s, but quad core instead of single core. And 64 bit. So maybe the closest comparison is the original Core 2 Duo MacBook Air, which ran at 1.6 MHz (for about 4 seconds before it throttled to 1.2 GHz, which the RISC-V shouldn't do).

Or, in the Arm world, a bit slower than a Pi 4, but a lot better than a Pi 3 (especially because 8 GB RAM and PCIe/M.2 not 1 GB and SD card).

I'd expect a 2nd generation motherboard fairly quickly. If it comes in the next six months (Eswin EIC7700) then probably about the speed of a mid-range Core 2 Quad. If mid next year (SG2380) then early i7.