I think this could be an amazing buy. €300k for the site and stick €500k into the build? You could possibly try go to 3 stories with a flat roof as the houses along that road are relatively tall (high pitched attics).
You could do something like Odos designed on Alma Road Monkstown or you could possibly try for some sort of Miami 3 level minimalist thingy with a single lane pool running the length of the basement partially under a glass floored entrance hall & porch.
Regardless, it’s a unique site so as you say, hopefully someone does something creative on it.