https://derpibooru.org/search?q=seapony

Well,there it is. No more differences between gen 4 and gen 5 versions. The whole umbrella of variations among them has been boiled down to a single seapony tag. 

It simplifies everything and all the diversity that may appear amongst them is reduced to this tag alone (except the gen 1 version). 

Potential controversies (implying that there were any in the first place) about what qualifies or not as seapony should most likely decrease from now on. 

In conclusion, everyone can relax and use the term freely, with a huge margin of flexibility.