Hardware shortcomings

[moonwalkers]

Err, modern motherboards make it a LOT harder to brick by writing wrong bios/firmware
(with a backup bios)
One can legitimately complain about somewhat defective uboots that are only tested
with one distro and can somewhat brick the device when booting something else
(because the pbp has a battery, it can 'remember' a bad setup, requiring a hard reset & a uboot change)
(and it is a bit of a pain when the emmc must be disabled/removed or defective switches
to short the SPI clock if you are so brave as to write to SPI)

Modern motherboards DO NOT use BIOS, they use UEFI with CSM module (that nowadays usually turned off out of the box) for backwards compatibility with bootloaders and OSes that don't understand UEFI specification.

U-boot compatibility issues are not so much with the distros, as much as with the individual kernels - switch around the kernel while keeping the rest of the distro the same and you can indeed get an issue, swap around the whole distro while keeping the kernel and you'll only get userland-specific issues. But also swap your kernel for a wrong one on an x86 system, one that lacks particular binary blob for the hardware present, and you can also get a system that fails to get basic functionality working. If you never ran into that situation - you're very lucky you never had to just work with whatever junk gets thrown your way.

Maybe I never did anything wrong on PBP (pretty sure that's not the case, though I have been pretty conservative about u-boot changes), but I never ran into boot issues because of the battery and it "remembering" anything. 4 seconds holding power button and then brief press - system is booting fresh. Problem is that there are two locations (if SPI is empty) where it reads u-boot, and from what I understand (perhaps incorrectly), u-boot on microSD can override u-boot on eMMC if u-boot on eMMC is configured to redirect the SoC to boot from microSD first.

Disabling eMMC (that has a simple switch on the mobo) is order of magnitude simpler than what we had to do back in 2005 with BIOS on a mobo - my roommate in uni had a bad flash. Luckily, a friend of ours had exactly the same mobo. We borrowed his BIOS chip, inserted it into my roommate's mobo, booted up the system, then on a live system pulled the BIOS ROM chip from the mobo, replaced it with the bad one, and re-flashed it. That's an order of magnitude more hassle than having to boot PBP from microSD with eMMC disabled, enabling eMMC, and replacing u-boot there. But yes, you're correct - modern x86 motherboards (which, again, about a decade since no longer use BIOS) have all kinds of protections against bad updates.