So, you would see them for this special that aired in 1986 and you would never see the seahorse version of it beyond this gimmick.

Easy comes,easy goes. That´s exactly what happened and the short term plan that was applied by Hasbro didn´t get any relevant impact in which they would use them again. In the wiki however, there were mermares that appeared in generation 3.5 but considering that said "gen" isn´t seen in a good light (not even among the hardcore fans who are interested in revisiting the archives dare to talk about this).

Their impact was almost non existent and unless I have the number of sales that occurred in 1984 (in 1986, the special aired on TV, I´ve got to fix this) when it comes to this toyline, this species mattered from almost zero to nothing despite being the pilot special that would introduce this 1st generation.

Do you see any appearances beyond the pilot and very short cameos (The Magic Coins) from this species? Well, I am advancing to you that they were absolute absent in the following decades.

It wasn´t until someone called Lauren Faust would get some inspiration of this gen while creating what would define the 4th generation. Even when she wasn´t around and left the team while producing the 2nd season, you can still see that gen 4 displayed an interest for reviving the 1st generation. Tirek would make his debut in Twilight´s Kingdom (S4 E25-E26) and the Smooze would appear (in a very different manner though) in Make New Friends but Keep Discord (S5 E08)

As for the fans reception, it didn´t go beyond the usual meme really. In fact, you look at the tags of the gen 1 characters and all of them are surpassed by a remagined version of them ,by using Lyra Heartstrings as the biggest icon instead (without any limbs whatsoever).

So there it goes the whole impact that happened throughout the years.That´s their entire legacy that was left and you see at those characters and they don´t even surpass the two digits. Most drawings related to this species have recreations of gen 4 characters applied to the seahors design. Because after all, they eyes and their appearance left a weird impression.