I've definitely thought about this concept and mentioned it in passing (probably in one of the preview or expansion announcement threads). Controlled Native Village variants are something that I keep returning to (I think the first fan card idea I ever posted on f.ds was one).
I'd write it this way:
Happy Hour
$4 - Event
+1 Buy
Put a card from your hand on your Tavern mat.
In games using this, at the start of your turn, you may call a non-Reserve card on your Tavern mat, to play it.
So many commas just to follow convention.
This allows you to:
- play Treasure in the action phase, which simplifies the card while also adding neat combo potential.
- play Miser'd Copper if you want to. It would reduce the value of Miser for coins, of course.
- put a Reserve card onto the Tavern mat from your hand without playing it.
- insta-Island VP for the same cost as Island, minus 2VP from an actual Island.
And it lets you play pure Victory cards from the Tavern. I'm not sure what to do about that. Possibilities:
- Leave it. Playing VP would result in the card returning to your deck, nothing more.
- Leave it. You would just fail to play the card and it would stay on your Tavern mat.
- Restrict the event to non-Victory cards (losing the Island effect for VP).