RP-SMA was created some 20 yrs ago due to regulatory / law requirements...
it was meant to be HARDER for the end user to connect to a wifi device another (higher gain) antenna than what came bundled from the factory
now it does not make any sense, RP-SMA cables and pigtails are everywhere (and, yes, actually even easier to find than regular SMA...)
I think maybe we have here SMA because it is meant as an INTERNAL connector, as replacement for MMCX (bigger.. better).... you need a pigtail to the case / housing external wall, so you can take whatever you need in your case, SMA to RP-SMA, SMA to N, SMA to TNC
maybe mtik should decide and go for SMA or RP-SMA, but I don't see it as a BIG problem; maybe this particular PCB-mounted connector does not exist / was not available in acceptable qty as RP-SMA when manufacturing the first lot
if something has to be changed / added / improved, I would prefer:
- supporting 802.3af/at PoE in addition to 24V passive PoE (jumper selectable?)
- adding a GPS chip and its RF port (MMCX!)