What's wrong with another 4-8-4? I don't see the problem with it. The 4-8-4 is one of the best designs ever created. It's fast, powerful, and versatile. Shows some of the best in American engineering in the past.
You say the Niagara isn't anything special looks-wise, and this is true. It's average. But so is the FEF-3. The designs are very similar, both of them being ALCO products.
We also don't need another Hudson either, as that is what a J3a would be, just another Hudson.