You're right - Ironhide was the only new Voyager in wave 3 and ROTF Starscream was the only one in wave 4. And then we got a steady clip of 2 per wave. There are still a couple of more Bayverse Voyagers to do - we have Evasion Optimus and TLK Megatron leaked, and that still leaves Knight Optimus, Galvatron, Hound at minimum. If you wanted to get creative you could do DOTM Ironhide, or maybe a more obscure character like TLK Onslaught (doubtful). But yeah, the options are absolutely dwindling.