For most embedded work which needs to be reliable, the RPi is to much designed to a price, with enough tradeoffs making it an unattractive and ultimately more expensive option. In a PoC we did, we had to replace RPi's weekly in the field, racking up intervention costs. This completely disappeared the moment we switched to beaglebones.
I quite like the RPi for what it is, a cheap & fun platform offering a lot of possibilities to the masses, but I wouldn't consider it to be a serious embedded platform to target you can depend on. But I've used it as a video/slideshow player in real-world situations, where if they'd drop out, there aren't any real consequences (which most of the time were cards failing, and yes, the root-fs was read-only...)
Though must say TI AM3* boards (beagle’s) have good mainline Linux support and they appear to do all their work on public got repos. Now the iMX* boards seem nice but I haven’t really found a maker board variant.
I mean, I have the strong suspicion that the vast majority of RPi owners wouldn't be able to cite the name of a single alternative. Not a one. RPi's popularity eclipsed everything else (like Arduino in its heyday).
And even in your comment you haven't mentioned any alternative yourself, only that they exist. If you care about people using alternatives you should start with that. Actually, I should too, but the only Embedded Linux boards with a PCIe interface I've used are super expensive FPGA-based ones, so not really in the same category.