No bucket is ever "due" or "comes next". Inventory allocation is what Amtrak yield management does and its inner workings are a mystery. Inventory is rarely allocated across all buckets and frequently skips some.
@niemi24s just helps everyone by figuring out where the current bucket price points are and publishing it. That way you know where the current price is relative to the possible prices and how bad a deal you might be getting (and therefore whether or not to buy). I have developed very rough rules of thumb I use myself for gauging when and whether yield managers for a given train are likely to reallocate inventory into a lower bucket. Whether or not they actually do it, when they do it if they do it, and which buckets they reallocate inventory to are no sure thing and the best anyone can do is educated guessing.
In any case, it looks like they have reallocated inventory. All dates in April for the TE, except three, now have 5 Bedrooms, the entire inventory, available at the 5th bucket, $1951,down from the 6th bucket, $2216. The three dates with higher prices are 4/1, 4 Bedrooms at 6th bucket ($2216), 2/22, 4 Bedrooms at 6th bucket ($2216) and 4/4, 3 Bedrooms at 7th bucket ($2523). The situation is now reversed, with the SWC in April being mostly in the 6th bucket of $2216 with a few dates being in the 7th bucket, $2523.
Since this inventory is 11 months out, it looks to me like somebody or something zigged when they should have zagged when they released it, because it looks like almost a wholesale reversal between the two trains on very recently released inventory.
Finally, "Eaglet" and/or "Eaglette" are derisive diminutives because the Eagle is a crappy train. The leading contender for "worst long distance train". Plus it is short.