Echoes didn't match Awakening and Fates, but official word from Nintendo is that it "exceeded expectations," which is the opposite of poor. I imagine they factored in the disadvantages the game faced when calculating expectations—I mean, it released
right after the Switch, to name one.
This interview gives us a glimpse at their internal process behind Echoes:
https://kantopia.wordpress.com/2017/04/27/fire-emblem-echoes-dengeki-developer-interview-april-2017/
Bolded confirms that, should they exist, future remakes will be titled "Echoes." Really, the only things that'd give me pause with the development of more remakes is what FE16 looks like, how conducive that look will be to recreating old games, and most importantly how prohibitive HD development is on the Switch.
If they're able to push out Fire Emblems at a similar rate to the 3DS with reusable assets, I don't see why we wouldn't get more remakes, especially of 4, 5, and 6.