The phrasing on the Shell Defense ability for Tortles in the new Extra Life Tortle Package is slightly vague. The relevant parts are...
While in your shell... (bonuses)... the only action you can take is a bonus action to emerge from your shell.
However, when you take the bonus action to emerge from your shell you are no longer in your shell and no longer have the action restriction. Since the bonus action to emerge doesn't say "this ends your turn" or anything like that we have room for debate that the restriction on actions no longer applies.
It seems like the RAI is that you would get no actions on the turn you emerge, but RAW a debate could be made. Which reading should be correct? As DM you can do as you wish, but if any Adventurers League games are played it would be good to have this straight.