Gosh. Always hard to evaluate ridciulous abilities on a 7-drop because it's not quite "I win" level, but it sure gets to be close.

So this is "Drop an eldrazi into play", with a side order of "Dual wielding druids" (there aren't any in this set at time of writing; so that makes it even harder to evaluate) and an 'I wish' of "All creatures are druids, so I drop a leyline-bonded into play, which becomes another leyline bonded, each of which drop a pair of eldrazi-druids into play...

Looking at main mtg, most druids are cheap mana makers of course. Awakener Druid would get you 8 power - but 12 power for 7 mana aint great; green gets to do that vanilla without shenanigans. Gilt-Leaf Archdruid and aim for druid-threshold? Or just smaller druids for a lot of card draw?

Doesn't feel 7-worthy; but it is flexible. And who knows what this set will bring us. So maybe?

I think a better way to think of this is that it reduces the cost of your bomb by one or two mana and also gives you a 4/4. Strong, but not particularly splashy at this cost. Maybe if there was a Craterhoof Druid

The template can also be simplified a bunch. "When ~ ETBs, you may cast a green creature card from your hand without paying its mana cost. If you cast a Druid spell this way, copy it." There's even room for another ability or flavor text now

Usually this kind of effect would simply circumvent casting altogether and put the creature card onto the battlefield.