The thing with Eloy is that even when he was "good" he wasn't anything special. His two best years were just half seasons where he hit around 140 wRC+. When he managed to actually play 120 games or so, he was a 105-115 hitter.
So even in the best case scenario you are talking about a 115 wRC+ hitter with negative defense and baserunning. That's still useful bench player material, but for a team with a DH already entrenched it makes it a tough fit.
Ideally he accepts an assignment to Buffalo and comes up if Springer gets hurt.
I guess if he mashes they could option Lukes and keep Eloy? Platoon Eloy against lefties (regress the splits and it probably works out okay) and then put Springer in the field?