In the first case I'm dubious that MT7981B can handle usefully more than GigE with the usual small packets, firewall rules, anti-buffer bloat, QoS, numerous clients, and related that people expect of a router these days.
Seems to really limit the audience and shorten the useful life of a router to penny pinch. How about a $88 NanoPi with dual 2.5G, 4GB ram, 32GB eMMC, and wifi? Is it really worth $10 to have 1/4th the ram, 1/256th the storage, 1G instead of 2.5G and less CPU[0]?
I got similar with the faster RK3588, 8GB ram, dual 2.5 and 1G, and metal case for $120. I've been quite impressed, it's about half as fast as my xeon E3-1230 from years ago.
* >1G internet in a mostly or exclusively wifi home
* <=1G internet + a 2.5G LAN, so that ethernet <=> wifi and ethernet<=>SSD transfers are faster
The second scenario could actually fit me right now, but my ISP is expecting to roll out multi-gigabit options later this year year.
At any rate, I agree with everyone else, I would prefer two 2.5G ports.