Their commercial/industrial business has nothing to do with PMK, and I doubt their commercial/industrial clients even know that website exists, nor would they bother to visit it. Those clients deal directly with SP and bypass the web all together.
At this point, SP's revenue is about evenly split between commercial clients and what they call "retail" product (what we call custom mech community group buys). The backlog has nothing to do with giving any particular part of their business priority over another (usually), but rather with the time scale for production given the number of machines and staff they have to actually make the keycaps.
Seeing as how their retail schedule is currently backlogged out to August, with no reduction in upcoming keysets in sight, I'd say that SP has a healthy future ahead of it. Of course, a lot could change when the next recession hits and things like custom keycap sets become unnecessary luxuries for many of the more recent enthusiasts.